Introduction to Unix

Frank G. Fiamingo

Linda DeBula

Linda Condron

University Technology Services

The Ohio State University

September 23, 1998
© 1996-1998 University Technology Services, The Ohio State University, Baker Systems Engineering
Building, 1971 Neil Avenue, Columbus, OH 43210.
All rights reserved. Redistribution and use, with or without modification, are permitted provided that the following
conditions are met:
1. Redistributions must retain the above copyright notice, this list of conditions, and the following disclaimer.
2. Neither the name of the University nor the names of its contributors may be used to endorse or promote
products or services derived from this document without specific prior written permission.
THIS PUBLICATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. THIS PUBLICATION MAY
INCLUDE TECHNICAL INACCURACIES OR TYPOGRAPHICAL ERRORS.

UNIX is a registered trademark of The Open Group, AT&T is a trademark of American Telephone and
Telegraph, Inc.

This publication is provided “as is” without warranty of any kind. This publication may include
technical inaccuracies or typographical errors.

Copyright and URLs revised September 1998

The authors’ email addresses are:

Frank Fiamingo fiamingo.1@osu.edu
Linda DeBula debula.2@osu.edu
Linda Condron condron.1@osu.edu

This document can be obtained via:

http://wks.uts.ohio-state.edu/unix_course/unix.html
or
ftp://wks.uts.ohio-state.edu/unix_course/unix_book.ps

2  1998 University Technology Services, The Ohio State University Introduction to Unix
 Table of Contents

1 History of Unix ..............................................................................7

2 Unix Structure ...............................................................................9
2.1 The Operating System ..................................................................9
2.2 The File System ...........................................................................11
2.3 Unix Directories, Files and Inodes .............................................12
2.4 Unix Programs ............................................................................13
3 Getting Started ............................................................................14
3.1 Logging in ....................................................................................14
3.1.1 Terminal Type .............................................................14
3.1.2 Passwords ....................................................................15
3.1.3 Exiting .........................................................................15
3.1.4 Identity ........................................................................16
3.2 Unix Command Line Structure .................................................16
3.3 Control Keys ................................................................................17
3.4 stty - terminal control .................................................................17
3.5 Getting Help ................................................................................19
3.6 Directory Navigation and Control .............................................20
3.6.1 pwd - print working directory .....................................21
3.6.2 cd - change directory ...................................................21
3.6.3 mkdir - make a directory .............................................22
3.6.4 rmdir - remove directory .............................................22
3.6.5 ls - list directory contents ............................................23
3.7 File Maintenance Commands ....................................................25
3.7.1 cp - copy a file .............................................................26
3.7.2 mv - move a file ..........................................................26
3.7.3 rm - remove a file ........................................................27
3.7.4 File Permissions ..........................................................27
3.7.5 chmod - change file permissions .................................28
3.7.6 chown - change ownership ..........................................29
3.7.7 chgrp - change group ..................................................29
3.8 Display Commands .....................................................................30
3.8.1 echo - echo a statement ...............................................30

Introduction to Unix  1998 University Technology Services, The Ohio State University 3
 3.8.2 cat - concatenate a file .................................................31
3.8.3 more, less, and pg - page through a file ......................31
3.8.4 head - display the start of a file ...................................32
3.8.5 tail - display the end of a file ......................................32
4 System Resources & Printing ....................................................33
4.1 System Resources ........................................................................33
4.1.1 df - summarize disk block and file usage ....................34
4.1.2 du - report disk space in use ........................................34
4.1.3 ps - show status of active processes ............................35
4.1.4 kill - terminate a process .............................................36
4.1.5 who - list current users ................................................37
4.1.6 whereis - report program locations ............................37
4.1.7 which - report the command found .............................38
4.1.8 hostname/uname - name of machine ...........................38
4.1.9 script - record your screen I/O ....................................38
4.1.10 date - current date and time .........................................40
4.2 Print Commands .........................................................................41
4.2.1 lp/lpr - submit a print job ............................................41
4.2.2 lpstat/lpq - check the status of a print job ...................42
4.2.3 cancel/lprm - cancel a print job ...................................42
4.2.4 pr - prepare files for printing .......................................43
5 Shells ............................................................................................45
5.1 Built-in Commands .....................................................................46
5.1.1 Sh ................................................................................46
5.1.2 Csh ..............................................................................47
5.2 Environment Variables ..............................................................48
5.3 The Bourne Shell, sh ...................................................................49
5.4 The C Shell, csh ...........................................................................50
5.5 Job Control ..................................................................................51
5.6 History ..........................................................................................52
5.7 Changing your Shell ...................................................................54
6 Special Unix Features .................................................................55
6.1 File Descriptors ...........................................................................55
6.2 File Redirection ...........................................................................55
6.2.1 Csh ..............................................................................56
6.2.2 Sh ................................................................................57
6.3 Other Special Command Symbols .............................................58
6.4 Wild Cards ...................................................................................58
7 Text Processing ............................................................................59
7.1 Regular Expression Syntax ........................................................59
7.2 Text Processing Commands .......................................................61
7.2.1 grep .............................................................................61
7.2.2 sed ...............................................................................65

4  1998 University Technology Services, The Ohio State University Introduction to Unix
 7.2.3 awk, nawk, gawk .........................................................67
8 Other Useful Commands ............................................................70
8.1 Working With Files ....................................................................70
8.1.1 cmp - compare file contents ........................................71
8.1.2 diff - differences in files ..............................................72
8.1.3 cut - select parts of a line ............................................73
8.1.4 paste - merge files .......................................................74
8.1.5 touch - create a file ......................................................76
8.1.6 wc - count words in a file ............................................77
8.1.7 ln - link to another file ................................................78
8.1.8 sort - sort file contents .................................................79
8.1.9 tee - copy command output .........................................82
8.1.10 uniq - remove duplicate lines ......................................84
8.1.11 strings - find ASCII strings .........................................85
8.1.12 file - file type ...............................................................86
8.1.13 tr - translate characters ................................................86
8.1.14 find - find files ............................................................89
8.2 File Archiving, Compression and Conversion .........................91
8.2.1 File Compression ........................................................91
8.2.2 tar - archive files .........................................................93
8.2.3 uuencode/uudecode - encode a file .............................94
8.2.4 dd - block copy and convert ........................................95
8.2.5 od - octal dump of a file ..............................................96
8.3 Remote Connections ...................................................................98
8.3.1 TELNET and FTP - remote login and file transfer protocols 98
8.3.2 finger - get information about users ..........................100
8.3.3 Remote commands ....................................................101
9 Shell Programming ...................................................................103
9.1 Shell Scripts ...............................................................................103
9.2 Setting Parameter Values .........................................................103
9.3 Quoting ......................................................................................104
9.4 Variables ....................................................................................105
9.5 Parameter Substitution ............................................................107
9.6 Here Document ..........................................................................109
9.7 Interactive Input .......................................................................110
9.7.1 Sh ..............................................................................110
9.7.2 Csh ............................................................................110
9.8 Functions ....................................................................................111
9.9 Control Commands ...................................................................113
9.9.1 Conditional if ............................................................113
9.9.1.1 Sh ........................................................................113
9.9.1.2 Csh ......................................................................114
9.9.2 Conditional switch and case ......................................115
9.9.2.1 Sh ........................................................................115

Introduction to Unix  1998 University Technology Services, The Ohio State University 5
 9.9.2.2 Csh ......................................................................116
9.9.3 for and foreach ..........................................................117
9.9.3.1 Sh ........................................................................117
9.9.3.2 Csh ......................................................................117
9.9.4 while ..........................................................................118
9.9.4.1 Sh ........................................................................118
9.9.4.2 Csh ......................................................................119
9.9.5 until ...........................................................................119
9.9.6 test .............................................................................120
9.9.7 C Shell Logical and Relational Operators ................122
10 Editors ........................................................................................123
10.1 Configuring Your vi Session ....................................................124
10.2 Configuring Your emacs Session .............................................125
10.3 vi Quick Reference Guide ........................................................126
10.4 emacs Quick Reference Guide ..............................................127
11 Unix Command Summary .......................................................128
11.1 Unix Commands ........................................................................128
12 A Short Unix Bibliography ......................................................131
12.1 Highly Recommended ...............................................................131
12.2 Assorted Others .........................................................................131

6  1998 University Technology Services, The Ohio State University Introduction to Unix
CHAPTER 1 History of Unix

1965 Bell Laboratories joins with MIT and General Electric in the development effort for the new
operating system, Multics, which would provide multi-user, multi-processor, and multi-level
(hierarchical) file system, among its many forward-looking features.
1969 AT&T was unhappy with the progress and drops out of the Multics project. Some of the Bell
Labs programmers who had worked on this project, Ken Thompson, Dennis Ritchie, Rudd Canaday,
and Doug McIlroy designed and implemented the first version of the Unix File System on a PDP-7
along with a few utilities. It was given the name UNIX by Brian Kernighan as a pun on Multics.

1970, Jan 1 time zero for UNIX

1971 The system now runs on a PDP-11, with 16Kbytes of memory, including 8Kbytes for user
programs and a 512Kbyte disk.

Its first real use is as a text processing tool for the patent department at Bell Labs. That utilization
justified further research and development by the programming group. UNIX caught on among
programmers because it was designed with these features:
• programmers environment
• simple user interface
• simple utilities that can be combined to perform powerful functions
• hierarchical file system
• simple interface to devices consistent with file format
• multi-user, multi-process system
• architecture independent and transparent to the user.

1973 Unix is re-written mostly in C, a new language developed by Dennis Ritchie. Being written in
this high-level language greatly decreased the effort needed to port it to new machines.

1974 Thompson and Ritchie publish a paper in the Communications of the ACM describing the
new Unix OS. This generates enthusiasm in the Academic community which sees a potentially great
teaching tool for studying programming systems development. Since AT&T is prevented from
marketing the product due to the 1956 Consent Decree they license it to Universities for educational
purposes and to commercial entities.

1977 There are now about 500 Unix sites world-wide.

Introduction to Unix  1998 University Technology Services, The Ohio State University 7
 History of Unix

1980 BSD 4.1 (Berkeley Software Development)

1983 SunOS, BSD 4.2, SysV

1984 There are now about 100,000 Unix sites running on many different hardware platforms, of
vastly different capabilities.

1988 AT&T and Sun Microsystems jointly develop System V Release 4 (SVR4). This would later
be developed into UnixWare and Solaris 2.

1993 Novell buys UNIX from AT&T

1994 Novell gives the name "UNIX" to X/OPEN

1995 Santa Cruz Operations buys UnixWare from Novell. Santa Cruz Operations and
Hewlett-Packard announce that they will jointly develop a 64-bit version of Unix.

1996 International Data Corporation forecasts that in 1997 there will be 3 million Unix systems
shipped world-wide.

8  1998 University Technology Services, The Ohio State University Introduction to Unix
 The Operating System

CHAPTER 2 Unix Structure

2.1 The Operating System

Unix is a layered operating system. The innermost layer is the hardware that provides the services for
the OS. The operating system, referred to in Unix as the kernel, interacts directly with the hardware
and provides the services to the user programs. These user programs don’t need to know anything
about the hardware. They just need to know how to interact with the kernel and it’s up to the kernel
to provide the desired service. One of the big appeals of Unix to programmers has been that most
well written user programs are independent of the underlying hardware, making them readily portable
to new systems.

User programs interact with the kernel through a set of standard system calls. These system calls
request services to be provided by the kernel. Such services would include accessing a file: open
close, read, write, link, or execute a file; starting or updating accounting records; changing ownership
of a file or directory; changing to a new directory; creating, suspending, or killing a process; enabling
access to hardware devices; and setting limits on system resources.

Unix is a multi-user, multi-tasking operating system. You can have many users logged into a
system simultaneously, each running many programs. It’s the kernel’s job to keep each process and
user separate and to regulate access to system hardware, including cpu, memory, disk and other I/O
devices.

Introduction to Unix  1998 University Technology Services, The Ohio State University 9
 Unix Structure

FIGURE 2.1 Unix System Structure

Programs

Kernel

Hardware

System Calls

10  1998 University Technology Services, The Ohio State University Introduction to Unix
 The File System

2.2 The File System

The Unix file system looks like an inverted tree structure. You start with the root directory, denoted
by /, at the top and work down through sub-directories underneath it.

FIGURE 2.2 Unix File Structure

bin dev etc lib tmp usr home

ttya cua0
bin lib local

passwd group
sh date csh
condron frank lindadb

source mail bin

xntp traceroute

Introduction to Unix  1998 University Technology Services, The Ohio State University 11
 Unix Structure

Each node is either a file or a directory of files, where the latter can contain other files and
directories. You specify a file or directory by its path name, either the full, or absolute, path name or
the one relative to a location. The full path name starts with the root, /, and follows the branches of
the file system, each separated by /, until you reach the desired file, e.g.:

/home/condron/source/xntp

A relative path name specifies the path relative to another, usually the current working directory that
you are at. Two special directory entries should be introduced now:

. the current directory

.. the parent of the current directory

So if I’m at /home/frank and wish to specify the path above in a relative fashion I could use:

../condron/source/xntp

This indicates that I should first go up one directory level, then come down through the condron
directory, followed by the source directory and then to xntp.

2.3 Unix Directories, Files and Inodes

Every directory and file is listed in its parent directory. In the case of the root directory, that parent
is itself. A directory is a file that contains a table listing the files contained within it, giving file
names to the inode numbers in the list. An inode is a special file designed to be read by the kernel to
learn the information about each file. It specifies the permissions on the file, ownership, date of
creation and of last access and change, and the physical location of the data blocks on the disk
containing the file.

The system does not require any particular structure for the data in the file itself. The file can be
ASCII or binary or a combination, and may represent text data, a shell script, compiled object code
for a program, directory table, junk, or anything you would like.

There’s no header, trailer, label information or EOF character as part of the file.

12  1998 University Technology Services, The Ohio State University Introduction to Unix
 Unix Programs

2.4 Unix Programs

A program, or command, interacts with the kernel to provide the environment and perform the
functions called for by the user. A program can be: an executable shell file, known as a shell script; a
built-in shell command; or a source compiled, object code file.
The shell is a command line interpreter. The user interacts with the kernel through the shell. You can
write ASCII (text) scripts to be acted upon by a shell.

System programs are usually binary, having been compiled from C source code. These are located in
places like /bin, /usr/bin, /usr/local/bin, /usr/ucb, etc. They provide the functions that you normally
think of when you think of Unix. Some of these are sh, csh, date, who, more, and there are many
others.

Introduction to Unix  1998 University Technology Services, The Ohio State University 13
 Getting Started

CHA P TE R 3 Getting Started

3.1 Logging in

After connecting with a Unix system, a user is prompted for a login username, then a password. The
login username is the user's unique name on the system. The password is a changeable code known
only to the user. At the login prompt, the user should enter the username; at the password prompt,
the current password should be typed.

Note: Unix is case sensitive. Therefore, the login and password should be typed exactly as issued;
the login, at least, will normally be in lower case.

3.1.1 Terminal Type

Most systems are set up so the user is by default prompted for a terminal type, which should be set to
match the terminal in use before proceeding. Most computers work if you choose "vt100". Users
connecting using a Sun workstation may want to use "sun"; those using an X-Terminal may want to
use "xterms" or "xterm".

The terminal type indicates to the Unix system how to interact with the session just opened.

Should you need to reset the terminal type, enter the command:
setenv TERM <term type> - if using the C-shell (see Chapter 4.)
(On some systems, e.g. MAGNUS, it’s also necessary to type "unsetenv TERMCAP".)
-or-
TERM=<term type>; export TERM - if using the Bourne shell (see Chapter 4.)

where <term type> is the terminal type, such as vt100, that you would like set.

14  1998 University Technology Services, The Ohio State University Introduction to Unix
 Logging in

3.1.2 Passwords

When your account is issued, you will be given an initial password. It is important for system and
personal security that the password for your account be changed to something of your choosing. The
command for changing a password is "passwd". You will be asked both for your old password and to
type your new selected password twice. If you mistype your old password or do not type your new
password the same way twice, the system will indicate that the password has not been changed.

Some system administrators have installed programs that check for appropriateness of password (is it
cryptic enough for reasonable system security). A password change may be rejected by this program.

When choosing a password, it is important that it be something that could not be guessed -- either by
somebody unknown to you trying to break in, or by an acquaintance who knows you. Suggestions for
choosing and using a password follow:
Don't use a word (or words) in any language
use a proper name
use information that can be found in your wallet
use information commonly known about you (car license, pet name, etc)
use control characters. Some systems can't handle them
write your password anywhere
ever give your password to *anybody*
Do use a mixture of character types (alphabetic, numeric, special)
use a mixture of upper case and lower case
use at least 6 characters
choose a password you can remember
change your password often
make sure nobody is looking over your shoulder when you are entering your password

3.1.3 Exiting
^D - indicates end of data stream; can log a user off. The latter is disabled on many systems
^C - interrupt
logout - leave the system
exit - leave the shell

Introduction to Unix  1998 University Technology Services, The Ohio State University 15
 Getting Started

3.1.4 Identity
The system identifies you by the user and group numbers (userid and groupid, respectively)
assigned to you by your system administrator. You don’t normally need to know your userid or
groupid as the system translates username ↔ userid, and groupname ↔ groupid automatically. You
probably already know your username; it’s the name you logon with. The groupname is not as
obvious, and indeed, you may belong to more than one group. Your primary group is the one
associated with your username in the password database file, as set up by your system administrator.
Similarly, there is a group database file where the system administrator can assign you rights to
additional groups on the system.

In the examples below % is your shell prompt; you don’t type this in.

You can determine your userid and the list of groups you belong to with the id and groups
commands. On some systems id displays your user and primary group information, e.g.:
% id
uid=1101(frank) gid=10(staff)

on other systems it also displays information for any additional groups you belong to:
% id
uid=1101(frank) gid=10(staff) groups=10(staff),5(operator),14(sysadmin),110(uts)

The groups command displays the group information for all the groups you belong to, e.g.:
% groups
staff sysadmin uts operator

3.2 Unix Command Line Structure

A command is a program that tells the Unix system to do something. It has the form:
command [options] [arguments]
where an argument indicates on what the command is to perform its action, usually a file or series of
files. An option modifies the command, changing the way it performs.
Commands are case sensitive. command and Command are not the same.
Options are generally preceded by a hyphen (-), and for most commands, more than one option can be
strung together, in the form:
command -[option][option][option]
e.g.:
ls -alR
will perform a long list on all files in the current directory and recursively perform the list through all
sub-directories.
For most commands you can separate the options, preceding each with a hyphen, e.g.:
command -option1 -option2 -option3

16  1998 University Technology Services, The Ohio State University Introduction to Unix
 Control Keys

as in:
ls -a -l -R
Some commands have options that require parameters. Options requiring parameters are usually
specified separately, e.g.:
lpr -Pprinter3 -# 2 file
will send 2 copies of file to printer3.
These are the standard conventions for commands. However, not all Unix commands will follow the
standard. Some don’t require the hyphen before options and some won’t let you group options
together, i.e. they may require that each option be preceded by a hyphen and separated by whitespace
from other options and arguments.
Options and syntax for a command are listed in the man page for the command.

3.3 Control Keys

Control keys are used to perform special functions on the command line or within an editor. You
type these by holding down the Control key and some other key simultaneously. This is usually
represented as ^Key. Control-S would be written as ^S. With control keys upper and lower case are
the same, so ^S is the same as ^s. This particular example is a stop signal and tells the terminal to
stop accepting input. It will remain that way until you type a start signal, ^Q.

Control-U is normally the "line-kill" signal for your terminal. When typed it erases the entire input
line.

In the vi editor you can type a control key into your text file by first typing ^V followed by the control
character desired, so to type ^H into a document type ^V^H.

3.4 stty - terminal control

stty reports or sets terminal control options. The "tty" is an abbreviation that harks back to the days
of teletypewriters, which were associated with transmission of telegraph messages, and which were
models for early computer terminals.

For new users, the most important use of the stty command is setting the erase function to the
appropriate key on their terminal. For systems programmers or shell script writers, the stty command
provides an invaluable tool for configuring many aspects of I/O control for a given device, including
the following:
- erase and line-kill characters
- data transmission speed
- parity checking on data transmission
- hardware flow control
- newline (NL) versus carriage return plus linefeed (CR-LF)

Introduction to Unix  1998 University Technology Services, The Ohio State University 17
 Getting Started

- interpreting tab characters

- edited versus raw input
- mapping of upper case to lower case

This command is very system specific, so consult the man pages for the details of the stty command
on your system.

Syntax
stty [options]

Options
(none) report the terminal settings
all (or -a) report on all options
echoe echo ERASE as BS-space-BS
dec set modes suitable for Digital Equipment Corporation operating systems (which
distinguishes between ERASE and BACKSPACE) (Not available on all systems)
kill set the LINE-KILL character
erase set the ERASE character
intr set the INTERRUPT character

Examples

You can display and change your terminal control settings with the stty command. To display all (-a)
of the current line settings:
% stty -a
speed 38400 baud, 24 rows, 80 columns
parenb -parodd cs7 -cstopb -hupcl cread -clocal -crtscts
-ignbrk brkint ignpar -parmrk -inpck istrip -inlcr -igncr icrnl -iuclc
ixon -ixany -ixoff imaxbel
isig iexten icanon -xcase echo echoe echok -echonl -noflsh -tostop
echoctl -echoprt echoke
opost -olcuc onlcr -ocrnl -onocr -onlret -ofill -ofdel
erase kill werase rprnt flush lnext susp intr quit stop eof
^H ^U ^W ^R ^O ^V ^Z/^Y ^C ^\ ^S/^Q ^D

You can change settings using stty, e.g., to change the erase character from ^? (the delete key) to ^H:
% stty erase ^H

This will set the terminal options for the current session only. To have this done for you
automatically each time you login, it can be inserted into the .login or .profile file that we’ll look at
later.

18  1998 University Technology Services, The Ohio State University Introduction to Unix
 Getting Help

3.5 Getting Help

The Unix manual, usually called man pages, is available on-line to explain the usage of the Unix
system and commands. To use a man page, type the command "man" at the system prompt followed
by the command for which you need information.

Syntax
man [options] command_name

Common Options
-k keyword list command synopsis line for all keyword matches
-M path path to man pages
-a show all matching man pages (SVR4)

Examples

You can use man to provide a one line synopsis of any commands that contain the keyword that you
want to search on with the "-k" option, e.g. to search on the keyword password, type:
% man -k password
passwd (5) - password file
passwd (1) - change password information

The number in parentheses indicates the section of the man pages where these references were found.
You can then access the man page (by default it will give you the lower numbered entry, but you can
use a command line option to specify a different one) with:
% man passwd
PASSWD(1) USER COMMANDS PASSWD(1)
NAME
passwd - change password information
SYNOPSIS
passwd [ -e login_shell ] [ username ]
DESCRIPTION
passwd changes (or sets) a user's password.
passwd prompts twice for the new password, without displaying
it. This is to allow for the possibility of typing mistakes.
Only the user and the super-user can change the user's password.
OPTIONS
-e Change the user's login shell.

Here we’ve paraphrased and truncated the output for space and copyright concerns.

Introduction to Unix  1998 University Technology Services, The Ohio State University 19
 Getting Started

3.6 Directory Navigation and Control

The Unix file system is set up like a tree branching out from the root. The the root directory of the
system is symbolized by the forward slash (/). System and user directories are organized under the
root. The user does not have a root directory in Unix; users generally log into their own home
directory. Users can then create other directories under their home. The following table summarizes
some directory navigation commands.

TABLE 3.1 Navigation and Directory Control Commands

Command/Syntax What it will do

cd [directory] change directory
ls [options] [directory or file] list directory contents or file permissions
mkdir [options] directory make a directory
pwd print working (current) directory
rmdir [options] directory remove a directory

If you’re familiar with DOS the following table comparing similar commands might help to provide
the proper reference frame.

TABLE 3.2 Unix vs DOS Navigation and Directory Control Commands

Command Unix DOS

list directory contents ls dir
make directory mkdir md & mkdir
change directory cd cd & chdir
delete (remove) directory rmdir rd & rmdir
return to user’s home directory cd cd\
location in path pwd cd
(present working directory)

20  1998 University Technology Services, The Ohio State University Introduction to Unix
 Directory Navigation and Control

3.6.1 pwd - print working directory

At any time you can determine where you are in the file system hierarchy with the pwd, print working
directory, command, e.g.:
% pwd
/home/frank/src

3.6.2 cd - change directory

You can change to a new directory with the cd, change directory, command. cd will accept both
absolute and relative path names.

Syntax
cd [directory]

Examples
cd (also chdir in some shells) change directory
cd changes to user's home directory
cd / changes directory to the system's root
cd .. goes up one directory level
cd ../.. goes up two directory levels
cd /full/path/name/from/root changes directory to absolute path named (note the leading slash)
cd path/from/current/location changes directory to path relative to current location (no leading
slash)
cd ~username/directory changes directory to the named username's indicated directory
(Note: the ~ is not valid in the Bourne shell; see Chapter 5.)

Introduction to Unix  1998 University Technology Services, The Ohio State University 21
 Getting Started

3.6.3 mkdir - make a directory

You extend your home hierarchy by making sub-directories underneath it. This is done with the
mkdir, make directory, command. Again, you specify either the full or relative path of the directory:

Syntax
mkdir [options] directory

Common Options
-p create the intermediate (parent) directories, as needed
-m mode access permissions (SVR4). (We’ll look at modes later in this Chapter).

Examples
% mkdir /home/frank/data

or, if your present working directory is /home/frank the following would be equivalent:
% mkdir data

3.6.4 rmdir - remove directory

A directory needs to be empty before you can remove it. If it’s not, you need to remove the files first.
Also, you can’t remove a directory if it is your present working directory; you must first change out
of it.

Syntax
rmdir directory

Examples
To remove the empty directory /home/frank/data while in /home/frank use:
% rmdir data

or
% rmdir /home/frank/data

22  1998 University Technology Services, The Ohio State University Introduction to Unix
 Directory Navigation and Control

3.6.5 ls - list directory contents

The command to list your directories and files is ls. With options it can provide information about the
size, type of file, permissions, dates of file creation, change and access.

Syntax
ls [options] [argument]

Common Options

When no argument is used, the listing will be of the current directory. There are many very useful
options for the ls command. A listing of many of them follows. When using the command, string the
desired options together preceded by "-".
-a lists all files, including those beginning with a dot (.).
-d lists only names of directories, not the files in the directory
-F indicates type of entry with a trailing symbol:
directories /
sockets =
symbolic links @
executables *
-g displays Unix group assigned to the file, requires the -l option (BSD only)
-or- on an SVR4 machine, e.g. Solaris, this option has the opposite effect
-L if the file is a symbolic link, lists the information for the file or directory the link
references, not the information for the link itself
-l long listing: lists the mode, link information, owner, size, last modification (time). If
the file is a symbolic link, an arrow (-->) precedes the pathname of the linked-to file.

The mode field is given by the -l option and consists of 10 characters. The first character is one of
the following:
CHARACTER IF ENTRY IS A
d directory
- plain file
b block-type special file
c character-type special file
l symbolic link
s socket

The next 9 characters are in 3 sets of 3 characters each. They indicate the file access permissions:
the first 3 characters refer to the permissions for the user, the next three for the users in the Unix
group assigned to the file, and the last 3 to the permissions for other users on the system.
Designations are as follows:

Introduction to Unix  1998 University Technology Services, The Ohio State University 23
 Getting Started

r read permission
w write permission
x execute permission
- no permission

There are a few less commonly used permission designations for special circumstances. These are
explained in the man page for ls.

Examples

To list the files in a directory:

% ls
demofiles frank linda

To list all files in a directory, including the hidden (dot) files try:
% ls -a
. .cshrc .history .plan .rhosts frank
.. .emacs .login .profile demofiles linda

To get a long listing:

% ls -al
total 24
drwxr-sr-x 5 workshop acs 512 Jun 7 11:12 .
drwxr-xr-x 6 root sys 512 May 29 09:59 ..
-rwxr-xr-x 1 workshop acs 532 May 20 15:31 .cshrc
-rw------- 1 workshop acs 525 May 20 21:29 .emacs
-rw------- 1 workshop acs 622 May 24 12:13 .history
-rwxr-xr-x 1 workshop acs 238 May 14 09:44 .login
-rw-r--r-- 1 workshop acs 273 May 22 23:53 .plan
-rwxr-xr-x 1 workshop acs 413 May 14 09:36 .profile
-rw------- 1 workshop acs 49 May 20 20:23 .rhosts
drwx------ 3 workshop acs 512 May 24 11:18 demofiles
drwx------ 2 workshop acs 512 May 21 10:48 frank
drwx------ 3 workshop acs 512 May 24 10:59 linda

24  1998 University Technology Services, The Ohio State University Introduction to Unix
 File Maintenance Commands

3.7 File Maintenance Commands

To create, copy, remove and change permissions on files you can use the following commands.

TABLE 3.3 File Maintenance Commands

Command/Syntax What it will do

chgrp [options] group file change the group of the file
chmod [options] file change file or directory access permissions
chown [options] owner file change the ownership of a file; can only be done by the superuser
cp [options] file1 file2 copy file1 into file2; file2 shouldn't already exist. This command creates
or overwrites file2.
mv [options] file1 file2 move file1 into file2
rm [options] file remove (delete) a file or directory (-r recursively deletes the directory
and its contents) (-i prompts before removing files)

If you’re familiar with DOS the following table comparing similar commands might help to provide
the proper reference frame.

TABLE 3.4 Unix vs DOS File Maintenance Commands

Command Unix DOS

copy file cp copy
move file mv move (not supported on all versions of DOS)
rename file mv rename & ren
delete (remove) file rm erase & del
display file to screen
entire file cat type
one page at a time more, less, pg type/p (not supported on all versions of DOS)

Introduction to Unix  1998 University Technology Services, The Ohio State University 25
 Getting Started

3.7.1 cp - copy a file

Copy the contents of one file to another with the cp command.

Syntax
cp [options] old_filename new_filename

Common Options
-i interactive (prompt and wait for confirmation before proceeding)
-r recursively copy a directory

Examples
% cp old_filename new_filename

You now have two copies of the file, each with identical contents. They are completely independent
of each other and you can edit and modify either as needed. They each have their own inode, data
blocks, and directory table entries.

3.7.2 mv - move a file

Rename a file with the move command, mv.

Syntax
mv [options] old_filename new_filename

Common Options
-i interactive (prompt and wait for confirmation before proceeding)
-f don’t prompt, even when copying over an existing target file (overrides -i)

Examples
% mv old_filename new_filename

You now have a file called new_filename and the file old_filename is gone. Actually all you’ve
done is to update the directory table entry to give the file a new name. The contents of the file remain
where they were.

26  1998 University Technology Services, The Ohio State University Introduction to Unix
 File Maintenance Commands

3.7.3 rm - remove a file

Remove a file with the rm, remove, command.

Syntax
rm [options] filename

Common Options
-i interactive (prompt and wait for confirmation before proceeding)
-r recursively remove a directory, first removing the files and subdirectories
beneath it
-f don’t prompt for confirmation (overrides -i)

Examples
% rm old_filename

A listing of the directory will now show that the file no longer exists. Actually, all you’ve done is to
remove the directory table entry and mark the inode as unused. The file contents are still on the disk,
but the system now has no way of identifying those data blocks with a file name. There is no
command to "unremove" a file that has been removed in this way. For this reason many novice users
alias their remove command to be "rm -i", where the -i option prompts them to answer yes or no
before the file is removed. Such aliases are normally placed in the .cshrc file for the C shell; see
Chapter 5)

3.7.4 File Permissions

Each file, directory, and executable has permissions set for who can read, write, and/or execute it.
To find the permissions assigned to a file, the ls command with the -l option should be used. Also,
using the -g option with "ls -l" will help when it is necessary to know the group for which the
permissions are set (BSD only).

When using the "ls -lg" command on a file (ls -l on SysV), the output will appear as follows:

-rwxr-x--- user unixgroup size Month nn hh:mm filename

The area above designated by letters and dashes (-rwxr-x---) is the area showing the file type and
permissions as defined in the previous Section. Therefore, a permission string, for example, of
-rwxr-x--- allows the user (owner) of the file to read, write, and execute it; those in the unixgroup of
the file can read and execute it; others cannot access it at all.

Introduction to Unix  1998 University Technology Services, The Ohio State University 27
 Getting Started

3.7.5 chmod - change file permissions

The command to change permissions on an item (file, directory, etc) is chmod (change mode). The
syntax involves using the command with three digits (representing the user (owner, u) permissions,
the group (g) permissions, and other (o) user's permissions) followed by the argument (which may
be a file name or list of files and directories). Or by using symbolic representation for the
permissions and who they apply to.

Each of the permission types is represented by either a numeric equivalent:

read=4, write=2, execute=1

or a single letter:
read=r, write=w, execute=x

A permission of 4 or r would specify read permissions. If the permissions desired are read and write,
the 4 (representing read) and the 2 (representing write) are added together to make a permission of 6.
Therefore, a permission setting of 6 would allow read and write permissions.

Alternatively, you could use symbolic notation which uses the one letter representation for who and
for the permissions and an operator, where the operator can be:
+ add permissions
- remove permissions
= set permissions

So to set read and write for the owner we could use "u=rw" in symbolic notation.

Syntax
chmod nnn [argument list] numeric mode
chmod [who]op[perm] [argument list] symbolic mode

where nnn are the three numbers representing user, group, and other permissions, who is any of u, g,
o, or a (all) and perm is any of r, w, x. In symbolic notation you can separate permission
specifications by commas, as shown in the example below.

Common Options
-f force (no error message is generated if the change is unsuccessful)
-R recursively descend through the directory structure and change the modes
Examples
If the permission desired for file1 is user: read, write, execute, group: read, execute, other: read,
execute, the command to use would be
chmod 755 file1 or chmod u=rwx,go=rx file1

28  1998 University Technology Services, The Ohio State University Introduction to Unix
 File Maintenance Commands

Reminder: When giving permissions to group and other to use a file, it is necessary to allow at least
execute permission to the directories for the path in which the file is located. The easiest way to do
this is to be in the directory for which permissions need to be granted:
chmod 711 . or chmod u=rw,+x . or chmod u=rwx,go=x .

where the dot (.) indicates this directory.

3.7.6 chown - change ownership

Ownership of a file can be changed with the chown command. On most versions of Unix this can
only be done by the super-user, i.e. a normal user can’t give away ownership of their files. chown is
used as below, where # represents the shell prompt for the super-user:

Syntax
chown [options] user[:group] file (SVR4)
chown [options] user[.group] file (BSD)

Common Options
-R recursively descend through the directory structure
-f force, and don’t report any errors

Examples
# chown new_owner file

3.7.7 chgrp - change group

Anyone can change the group of files they own, to another group they belong to, with the chgrp
command.

Syntax
chgrp [options] group file

Common Options
-R recursively descend through the directory structure
-f force, and don’t report any errors

Examples
% chgrp new_group file

Introduction to Unix  1998 University Technology Services, The Ohio State University 29
 Getting Started

3.8 Display Commands

There are a number of commands you can use to display or view a file. Some of these are editors
which we will look at later. Here we will illustrate some of the commands normally used to display a
file.

TABLE 3.5 Display Commands

Command/Syntax What it will do

cat [options] file concatenate (list) a file
echo [text string] echo the text string to stdout
head [-number] file display the first 10 (or number of) lines of a file
more (or less or pg) [options] file page through a text file
tail [options] file display the last few lines (or parts) of a file

3.8.1 echo - echo a statement

The echo command is used to repeat, or echo, the argument you give it back to the standard output
device. It normally ends with a line-feed, but you can specify an option to prevent this.

Syntax
echo [string]

Common Options
-n don’t print <new-line> (BSD, shell built-in)
\c don’t print <new-line> (SVR4)
\0n where n is the 8-bit ASCII character code (SVR4)
\t tab (SVR4)
\f form-feed (SVR4)
\n new-line (SVR4)
\v vertical tab (SVR4)

Examples
% echo Hello Class or echo "Hello Class"

To prevent the line feed:

% echo -n Hello Class or echo "Hello Class \c"

where the style to use in the last example depends on the echo command in use.

The \x options must be within pairs of single or double quotes, with or without other string characters.

30  1998 University Technology Services, The Ohio State University Introduction to Unix
 Display Commands

3.8.2 cat - concatenate a file

Display the contents of a file with the concatenate command, cat.

Syntax
cat [options] [file]

Common Options
-n precede each line with a line number
-v display non-printing characters, except tabs, new-lines, and form-feeds
-e display $ at the end of each line (prior to new-line) (when used with -v option)

Examples
% cat filename

You can list a series of files on the command line, and cat will concatenate them, starting each in turn,
immediately after completing the previous one, e.g.:
% cat file1 file2 file3

3.8.3 more, less, and pg - page through a file

more, less, and pg let you page through the contents of a file one screenful at a time. These may not
all be available on your Unix system. They allow you to back up through the previous pages and
search for words, etc.

Syntax
more [options] [+/pattern] [filename]
less [options] [+/pattern] [filename]
pg [options] [+/pattern] [filename]

Options
more less pg Action
-c -c -c clear display before displaying
-i ignore case
-w default default don’t exit at end of input, but prompt and wait
-lines -lines # of lines/screenful
+/pattern +/pattern +/pattern search for the pattern

Introduction to Unix  1998 University Technology Services, The Ohio State University 31
 Getting Started

Internal Controls
more displays (one screen at a time) the file requested
<space bar> to view next screen
<return> or <CR> to view one more line
q to quit viewing the file
h help
b go back up one screenful
/word search for word in the remainder of the file
See the man page for additional options
less similar to more; see the man page for options
pg the SVR4 equivalent of more (page)

3.8.4 head - display the start of a file

head displays the head, or start, of the file.

Syntax
head [options] file

Common Options
-n number number of lines to display, counting from the top of the file
-number same as above

Examples

By default head displays the first 10 lines. You can display more with the "-n number", or
"-number" options, e.g., to display the first 40 lines:
% head -40 filename or head -n 40 filename

3.8.5 tail - display the end of a file

tail displays the tail, or end, of the file.

Syntax
tail [options] file

Common Options
-number number of lines to display, counting from the bottom of the file

Examples

The default is to display the last 10 lines, but you can specify different line or byte numbers, or a
different starting point within the file. To display the last 30 lines of a file use the -number style:
% tail -30 filename

32  1998 University Technology Services, The Ohio State University Introduction to Unix
 System Resources

CHAPTER 4 System Resources &

Printing

4.1 System Resources

Commands to report or manage system resources.

TABLE 4.1 System Resource Commands

Command/Syntax What it will do

chsh (passwd -e/-s) username login_shell change the user’s login shell (often only by the superuser)
date [options] report the current date and time
df [options] [resource] report the summary of disk blocks and inodes free and in use
du [options] [directory or file] report amount of disk space in use+
hostname/uname display or set (super-user only) the name of the current machine
kill [options] [-SIGNAL] [pid#] [%job] send a signal to the process with the process id number (pid#) or job
control number (%n). The default signal is to kill the process.
man [options] command show the manual (man) page for a command
passwd [options] set or change your password
ps [options] show status of active processes
script file saves everything that appears on the screen to file until exit is executed
stty [options] set or display terminal control options
whereis [options] command report the binary, source, and man page locations for the command
named
which command reports the path to the command or the shell alias in use
who or w report who is logged in and what processes are running

Introduction to Unix  1998 University Technology Services, The Ohio State University 33
 System Resources & Printing

4.1.1 df - summarize disk block and file usage

df is used to report the number of disk blocks and inodes used and free for each file system. The
output format and valid options are very specific to the OS and program version in use.

Syntax
df [options] [resource]

Common Options
-l local file systems only (SVR4)
-k report in kilobytes (SVR4)

Examples
{unix prompt 1} df
Filesystem kbytes used avail capacity Mounted on
/dev/sd0a 20895 19224 0 102% /
/dev/sd0h 319055 131293 155857 46% /usr
/dev/sd1g 637726 348809 225145 61% /usr/local
/dev/sd1a 240111 165489 50611 77%
/home/guardian
peri:/usr/local/backup
1952573 976558 780758 56%
/usr/local/backup
peri:/home/peri 726884 391189 263007 60% /home/peri
peri:/usr/spool/mail 192383 1081 172064 1%
/var/spool/mail
peri:/acs/peri/2 723934 521604 129937 80% /acs/peri/2

4.1.2 du - report disk space in use

du reports the amount of disk space in use for the files or directories you specify.

Syntax
du [options] [directory or file]

Common Options
-a display disk usage for each file, not just subdirectories
-s display a summary total only
-k report in kilobytes (SVR4)

34  1998 University Technology Services, The Ohio State University Introduction to Unix
 System Resources

Examples
{unix prompt 3} du
1 ./.elm
1 ./Mail
1 ./News
20 ./uc
86 .

{unix prompt 4} du -a uc
7 uc/unixgrep.txt
5 uc/editors.txt
1 uc/.emacs
1 uc/.exrc
4 uc/telnet.ftp
1 uc/uniq.tee.txt
20 uc

4.1.3 ps - show status of active processes

ps is used to report on processes currently running on the system. The output format and valid
options are very specific to the OS and program version in use.

Syntax
ps [options]

Common Options
BSD SVR4
-a -e all processes, all users
-e environment/everything
-g process group leaders as well
-l -l long format
-u -u user user oriented report
-x -e even processes not executed from terminals
-f full listing
-w report first 132 characters per line

note -- Because the ps command is highly system-specific, it is recommended that you consult the
man pages of your system for details of options and interpretation of ps output.

Introduction to Unix  1998 University Technology Services, The Ohio State University 35
 System Resources & Printing

Examples
{unix prompt 5} ps
PID TT STAT TIME COMMAND
15549 p0 IW 0:00 -tcsh (tcsh)
15588 p0 IW 0:00 man nice
15594 p0 IW 0:00 sh -c less /tmp/man15588
15595 p0 IW 0:00 less /tmp/man15588
15486 p1 S 0:00 -tcsh (tcsh)
15599 p1 T 0:00 emacs unixgrep.txt
15600 p1 R 0:00 ps

4.1.4 kill - terminate a process

kill sends a signal to a process, usually to terminate it.

Syntax
kill [-signal] process-id

Common Options
-l displays the available kill signals:

Examples
{unix prompt 9} kill -l
HUP INT QUIT ILL TRAP IOT EMT FPE KILL BUS SEGV SYS PIPE ALRM TERM URG STOP
TSTP CONT CHLD TTIN TTOU IO XCPU XFSZ VTALRM PROF WINCH LOST USR1 USR2

The -KILL signal, also specified as -9 (because it is 9th on the above list), is the most commonly
used kill signal. Once seen, it can’t be ignored by the program whereas the other signals can.
{unix prompt 10} kill -9 15599
[1] + Killed emacs unixgrep.txt

36  1998 University Technology Services, The Ohio State University Introduction to Unix
 System Resources

4.1.5 who - list current users

who reports who is logged in at the present time.

Syntax
who [am i]

Examples
beauty condron>who
wmtell ttyp1 Apr 21 20:15 (apple.acs.ohio-s)
fbwalk ttyp2 Apr 21 23:21 (worf.acs.ohio-st)
stwang ttyp3 Apr 21 23:22 (127.99.25.8)
david ttyp4 Apr 21 22:27 (slip1-61.acs.ohi)
tgardner ttyp5 Apr 21 23:07 (picard.acs.ohio-)
awallace ttyp6 Apr 21 23:00 (ts31-4.homenet.o)
gtl27 ttyp7 Apr 21 23:24 (data.acs.ohio-st)
ccchang ttyp8 Apr 21 23:32 (slip3-10.acs.ohi)
condron ttypc Apr 21 23:38 (lcondron-mac.acs)
dgildman ttype Apr 21 22:30 (slip3-36.acs.ohi)
fcbetz ttyq2 Apr 21 21:12 (ts24-10.homenet.)

beauty condron>who am i
beauty!condron ttypc Apr 21 23:38 (lcondron-mac.acs)

4.1.6 whereis - report program locations

whereis reports the filenames of source, binary, and manual page files associated with command(s).

Syntax
whereis [options] command(s)

Common Options
-b report binary files only
-m report manual sections only
-s report source files only

Examples
brigadier: condron [69]> whereis Mail
Mail: /usr/ucb/Mail /usr/lib/Mail.help /usr/lib/Mail.rc /usr/man/man1/Mail.1

Introduction to Unix  1998 University Technology Services, The Ohio State University 37
 System Resources & Printing

brigadier: condron [70]> whereis -b Mail

Mail: /usr/ucb/Mail /usr/lib/Mail.help /usr/lib/Mail.rc

brigadier: condron [71]> whereis -m Mail

Mail: /usr/man/man1/Mail.1

4.1.7 which - report the command found

which will report the name of the file that is be executed when the command is invoked. This will be
the full path name or the alias that’s found first in your path.

Syntax
which command(s)

example--
brigadier: condron [73]> which Mail
/usr/ucb/Mail

4.1.8 hostname/uname - name of machine

hostname (uname -n on SysV) reports the host name of the machine the user is logged into, e.g.:
brigadier: condron [91]> hostname
brigadier

uname has additional options to print information about system hardware type and software version.

4.1.9 script - record your screen I/O

script creates a script of your session input and output. Using the script command, you can capture
all the data transmission from and to your terminal screen until you exit the script program. This can
be useful during the programming-and-debugging process, to document the combination of things
you have tried, or to get a printed copy of it all for later perusal.

Syntax
script [-a] [file] <. . .> exit

Common Options
-a append the output to file

typescript is the name of the default file used by script.

You must remember to type exit to end your script session and close your typescript file.

38  1998 University Technology Services, The Ohio State University Introduction to Unix
 System Resources

Examples
beauty condron>script
Script started, file is typescript
beauty condron>ps
PID TT STAT TIME COMMAND
23323 p8 S 0:00 -h -i (tcsh)
23327 p8 R 0:00 ps
18706 pa S 0:00 -tcsh (tcsh)
23315 pa T 0:00 emacs
23321 pa S 0:00 script
23322 pa S 0:00 script
3400 pb I 0:00 -tcsh (tcsh)
beauty condron>kill -9 23315
beauty condron>date
Mon Apr 22 22:29:44 EDT 1996
beauty condron>exit
exit
Script done, file is typescript
[1] + Killed emacs

beauty condron>cat typescript

Script started on Mon Apr 22 22:28:36 1996
beauty condron>ps
PID TT STAT TIME COMMAND
23323 p8 S 0:00 -h -i (tcsh)
23327 p8 R 0:00 ps
18706 pa S 0:00 -tcsh (tcsh)
23315 pa T 0:00 emacs
23321 pa S 0:00 script
23322 pa S 0:00 script
3400 pb I 0:00 -tcsh (tcsh)
beauty condron>kill -9 23315
beauty condron>date
Mon Apr 22 22:29:44 EDT 1996
beauty condron>exit
exit

script done on Mon Apr 22 22:30:02 1996

beauty condron>

Introduction to Unix  1998 University Technology Services, The Ohio State University 39
 System Resources & Printing

4.1.10 date - current date and time

date displays the current data and time. A superuser can set the date and time.

Syntax
date [options] [+format]

Common Options
-u use Universal Time (or Greenwich Mean Time)
+format specify the output format
%a weekday abbreviation, Sun to Sat
%h month abbreviation, Jan to Dec
%j day of year, 001 to 366
%n <new-line>
%t <TAB>
%y last 2 digits of year, 00 to 99
%D MM/DD/YY date
%H hour, 00 to 23
%M minute, 00 to 59
%S second, 00 to 59
%T HH:MM:SS time

Examples
beauty condron>date
Mon Jun 10 09:01:05 EDT 1996

beauty condron>date -u
Mon Jun 10 13:01:33 GMT 1996

beauty condron>date +%a%t%D

Mon 06/10/96

beauty condron>date '+%y:%j'

96:162

40  1998 University Technology Services, The Ohio State University Introduction to Unix
 Print Commands

4.2 Print Commands

TABLE 4.2 Printing Commands

Command/Syntax What it will do

lpq (lpstat) [options] show the status of print jobs
lpr (lp) [options] file print to defined printer
lprm (cancel) [options] remove a print job from the print queue
pr [options] [file] filter the file and print it on the terminal

The print commands allow us to print files to standard output (pr) or to a line printer (lp/lpr) while
filtering the output. The BSD and SysV printer commands use different names and different options
to produce the same results: lpr, lprm, and lpq vs lp, cancel, and lpstat for the BSD and SysV submit,
cancel, and check the status of a print job, respectively.

4.2.1 lp/lpr - submit a print job

lp and lpr submit the specified file, or standard input, to the printer daemon to be printed. Each job is
given a unique request-id that can be used to follow or cancel the job while it’s in the queue.

Syntax
lp [options] filename
lpr [options] filename

Common Options
lp lpr function
-n number -#number number of copies
-t title -Ttitle title for job
-d destination -Pprinter printer name
-c (default) copy file to queue before printing
(default) -s don’t copy file to queue before printing
-o option additional options, e.g. nobanner

Files beginning with the string "%!" are assumed to contain PostScript commands.

Examples

To print the file ssh.ps:

% lp ssh.ps
request id is lp-153 (1 file(s))

This submits the job to the queue for the default printer, lp, with the request-id lp-153.

Introduction to Unix  1998 University Technology Services, The Ohio State University 41
 System Resources & Printing

4.2.2 lpstat/lpq - check the status of a print job

You can check the status of your print job with lpstat or lpq.

Syntax
lpstat [options]
lpq [options] [job#] [username]

Common Options
lpstat lpq function
-d (defaults to lp) list system default destination
-s summarize print status
-t print all status information
-u [login-ID-list] user list
-v list printers known to the system
-p printer_dest -Pprinter_dest list status of printer, printer_dest

Examples
% lpstat
lp-153 frank 208068 Apr 29 15:14 on lp

4.2.3 cancel/lprm - cancel a print job

Any user can cancel only heir own print jobs.

Syntax
cancel [request-ID] [printer]
lprm [options] [job#] [username]

Common Options
cancel lprm function
-Pprinter specify printer
- all jobs for user
-u [login-ID-list] user list

Examples

To cancel the job submitted above:

% cancel lp-153

42  1998 University Technology Services, The Ohio State University Introduction to Unix
 Print Commands

4.2.4 pr - prepare files for printing

pr prints header and trailer information surrounding the formatted file. You can specify the number
of pages, lines per page, columns, line spacing, page width, etc. to print, along with header and trailer
information and how to treat <tab> characters.

Syntax
pr [options] file

Common Options
+page_number start printing with page page_number of the formatted input file
-column number of columns
-a modify -column option to fill columns in round-robin order
-d double spacing
-e[char][gap] tab spacing
-h header_string header for each page
-l lines lines per page
-t don’t print the header and trailer on each page
-w width width of page

Examples

The file containing the list of P. G. Wodehouse’s Lord Emsworth books could be printed, at 14 lines
per page (including 5 header and 5 (empty) trailer lines) below, where the -e option specifies the
<tab> conversion style:
% pr -l 14 -e42 wodehouse

Apr 29 11:11 1996 wodehouse_emsworth_books Page 1

Something Fresh [1915] Uncle Dynamite [1948]

Leave it to Psmith [1923] Pigs Have Wings [1952]
Summer Lightning [1929] Cocktail Time [1958]
Heavy Weather [1933] Service with a Smile [1961]

Introduction to Unix  1998 University Technology Services, The Ohio State University 43
 System Resources & Printing

Apr 29 11:11 1996 wodehouse_emsworth_books Page 2

Blandings Castle and Elsewhere [1935] Galahad at Blandings [1965]

Uncle Fred in the Springtime [1939] A Pelican at Blandings [1969]
Full Moon [1947] Sunset at Blandings [1977]

44  1998 University Technology Services, The Ohio State University Introduction to Unix
 Print Commands

CHAPTER 5 Shells

The shell sits between you and the operating system, acting as a command interpreter. It reads your
terminal input and translates the commands into actions taken by the system. The shell is analogous
to command.com in DOS. When you log into the system you are given a default shell. When the shell
starts up it reads its startup files and may set environment variables, command search paths, and
command aliases, and executes any commands specified in these files.

The original shell was the Bourne shell, sh. Every Unix platform will either have the Bourne shell, or
a Bourne compatible shell available. It has very good features for controlling input and output, but is
not well suited for the interactive user. To meet the latter need the C shell, csh, was written and is now
found on most, but not all, Unix systems. It uses C type syntax, the language Unix is written in, but
has a more awkward input/output implementation. It has job control, so that you can reattach a job
running in the background to the foreground. It also provides a history feature which allows you to
modify and repeat previously executed commands.

The default prompt for the Bourne shell is $ (or #, for the root user). The default prompt for the C shell
is %.

Numerous other shells are available from the network. Almost all of them are based on either sh or
csh with extensions to provide job control to sh, allow in-line editing of commands, page through
previously executed commands, provide command name completion and custom prompt, etc. Some
of the more well known of these may be on your favorite Unix system: the Korn shell, ksh, by David
Korn and the Bourne Again SHell, bash, from the Free Software Foundations GNU project, both based
on sh, the T-C shell, tcsh, and the extended C shell, cshe, both based on csh. Below we will describe
some of the features of sh and csh so that you can get started.

Introduction to Unix  1998 University Technology Services, The Ohio State University 45
 Shells

5.1 Built-in Commands

The shells have a number of built-in, or native commands. These commands are executed directly in
the shell and don’t have to call another program to be run. These built-in commands are different for
the different shells.

5.1.1 Sh
For the Bourne shell some of the more commonly used built-in commands are:
: null command
. source (read and execute) commands from a file
case case conditional loop
cd change the working directory (default is $HOME)
echo write a string to standard output
eval evaluate the given arguments and feed the result back to the shell
exec execute the given command, replacing the current shell
exit exit the current shell
export share the specified environment variable with subsequent shells
for for conditional loop
if if conditional loop
pwd print the current working directory
read read a line of input from stdin
set set variables for the shell
test evaluate an expression as true or false
trap trap for a typed signal and execute commands
umask set a default file permission mask for new files
unset unset shell variables
wait wait for a specified process to terminate
while while conditional loop

46  1998 University Technology Services, The Ohio State University Introduction to Unix
 Built-in Commands

5.1.2 Csh
For the C shell the more commonly used built-in functions are:
alias assign a name to a function
bg put a job into the background
cd change the current working directory
echo write a string to stdout
eval evaluate the given arguments and feed the result back to the shell
exec execute the given command, replacing the current shell
exit exit the current shell
fg bring a job to the foreground
foreach for conditional loop
glob do filename expansion on the list, but no "\" escapes are honored
history print the command history of the shell
if if conditional loop
jobs list or control active jobs
kill kill the specified process
limit set limits on system resources
logout terminate the login shell
nice command lower the scheduling priority of the process, command
nohup command do not terminate command when the shell exits
popd pop the directory stack and return to that directory
pushd change to the new directory specified and add the current one to the directory
stack
rehash recreate the hash table of paths to executable files
repeat repeat a command the specified number of times
set set a shell variable
setenv set an environment variable for this and subsequent shells
source source (read and execute) commands from a file
stop stop the specified background job
switch switch conditional loop
umask set a default file permission mask for new files
unalias remove the specified alias name
unset unset shell variables
unsetenv unset shell environment variables
wait wait for all background processes to terminate
while while conditional loop

Introduction to Unix  1998 University Technology Services, The Ohio State University 47
 Shells

5.2 Environment Variables

Environmental variables are used to provide information to the programs you use. You can have both
global environment and local shell variables. Global environment variables are set by your login
shell and new programs and shells inherit the environment of their parent shell. Local shell variables
are used only by that shell and are not passed on to other processes. A child process cannot pass a
variable back to its parent process.
The current environment variables are displayed with the "env" or "printenv" commands. Some
common ones are:
• DISPLAY The graphical display to use, e.g. nyssa:0.0
• EDITOR The path to your default editor, e.g. /usr/bin/vi
• GROUP Your login group, e.g. staff
• HOME Path to your home directory, e.g. /home/frank
• HOST The hostname of your system, e.g. nyssa
• IFS Internal field separators, usually any white space (defaults to tab, space
and <newline>)
• LOGNAME The name you login with, e.g. frank
• PATH Paths to be searched for commands, e.g. /usr/bin:/usr/ucb:/usr/local/bin
• PS1 The primary prompt string, Bourne shell only (defaults to $)
• PS2 The secondary prompt string, Bourne shell only (defaults to >)
• SHELL The login shell you’re using, e.g. /usr/bin/csh
• TERM Your terminal type, e.g. xterm
• USER Your username, e.g. frank
Many environment variables will be set automatically when you login. You can modify them or define
others with entries in your startup files or at anytime within the shell. Some variables you might want
to change are PATH and DISPLAY. The PATH variable specifies the directories to be automatically
searched for the command you specify. Examples of this are in the shell startup scripts below.
You set a global environment variable with a command similar to the following for the C shell:
% setenv NAME value
and for Bourne shell:
$ NAME=value; export NAME
You can list your global environmental variables with the env or printenv commands. You unset them
with the unsetenv (C shell) or unset (Bourne shell) commands.
To set a local shell variable use the set command with the syntax below for C shell. Without options
set displays all the local variables.
% set name=value
For the Bourne shell set the variable with the syntax:
$ name=value

The current value of the variable is accessed via the "$name", or "${name}", notation.

48  1998 University Technology Services, The Ohio State University Introduction to Unix
 The Bourne Shell, sh

5.3 The Bourne Shell, sh

Sh uses the startup file .profile in your home directory. There may also be a system-wide startup file,
e.g. /etc/profile. If so, the system-wide one will be sourced (executed) before your local one.
A simple .profile could be the following:
PATH=/usr/bin:/usr/ucb:/usr/local/bin:. # set the PATH
export PATH # so that PATH is available to subshells
# Set a prompt
PS1="{`hostname` `whoami`} " # set the prompt, default is "$"
# functions
ls() { /bin/ls -sbF "$@";}
ll() { ls -al "$@";}
# Set the terminal type
stty erase ^H # set Control-H to be the erase key
eval `tset -Q -s -m ':?xterm'` # prompt for the terminal type, assume xterm
#
umask 077
Whenever a # symbol is encountered the remainder of that line is treated as a comment. In the PATH
variable each directory is separated by a colon (:) and the dot (.) specifies that the current directory is
in your path. If the latter is not set it’s a simple matter to execute a program in the current directory
by typing:
./program_name
It’s actually a good idea not to have dot (.) in your path, as you may inadvertently execute a program
you didn’t intend to when you cd to different directories.
A variable set in .profile is set only in the login shell unless you "export" it or source .profile from
another shell. In the above example PATH is exported to any subshells. You can source a file with
the built-in "." command of sh, i.e.:
. ./.profile
You can make your own functions. In the above example the function ll results in an "ls -al" being
done on the specified files or directories.
With stty the erase character is set to Control-H (^H), which is usually the Backspace key.
The tset command prompts for the terminal type, and assumes "xterm" if we just hit <CR>. This
command is run with the shell built-in, eval, which takes the result from the tset command and uses it
as an argument for the shell. In this case the "-s" option to tset sets the TERM and TERMCAP
variables and exports them.
The last line in the example runs the umask command with the option such that any files or directories
you create will not have read/write/execute permission for group and other.
For further information about sh type "man sh" at the shell prompt.

Introduction to Unix  1998 University Technology Services, The Ohio State University 49
 Shells

5.4 The C Shell, csh

Csh uses the startup files .cshrc and .login. Some versions use a system-wide startup file, e.g.
/etc/csh.login. Your .login file is sourced (executed) only when you login. Your .cshrc file is sourced
every time you start a csh, including when you login. It has many similar features to .profile, but a
different style of doing things. Here we use the set or setenv commands to initialize a variable, where
set is used for this shell and setenv for this and any subshells. The environment variables: USER,
TERM, and PATH, are automatically imported to and exported from the user, term, and path
variables of the csh. So setenv doesn’t need to be done for these. The C shell uses the symbol, ~, to
indicate the user’s home directory in a path, as in ~/.cshrc, or to specify another user’s login directory,
as in ~username/.cshrc.
Predefined variables used by the C shell include:
• argv The list of arguments of the current shell
• cwd The current working directory
• history Sets the size of the history list to save
• home The home directory of the user; starts with $HOME
• ignoreeof When set ignore EOF (^D) from terminals
• noclobber When set prevent output redirection from overwriting existing files
• noglob When set prevent filename expansion with wildcard pattern matching
• path The command search path; starts with $PATH
• prompt Set the command line prompt (default is %)
• savehist number of lines to save in the history list to save in the .history file
• shell The full pathname of the current shell; starts with $SHELL
• status The exit status of the last command (0=normal exit, 1=failed
command)
• term Your terminal type, starts with $TERM
• user Your username, starts with $USER
A simple .cshrc could be:
set path=(/usr/bin /usr/ucb /usr/local/bin ~/bin . ) # set the path
set prompt = "{‘hostname‘ ‘whoami‘ !} " # set the primary prompt; default is "%"
set noclobber # don’t redirect output to existing files
set ignoreeof # ignore EOF (^D) for this shell
set history=100 savehist=50 # keep a history list and save it between logins
# aliases
alias h history # alias h to "history"
alias ls "/usr/bin/ls -sbF" # alias ls to "ls -sbF"
alias ll ls -al # alias ll to "ls -sbFal" (combining these options with those for "ls" above)
alias cd ’cd \!*;pwd’ # alias cd so that it prints the current working directory after the change
umask 077

50  1998 University Technology Services, The Ohio State University Introduction to Unix
 Job Control

Some new features here that we didn’t see in .profile are noclobber, ignoreeof, and history.
Noclobber indicates that output will not be redirected to existing files, while ignoreeof specifies that
EOF (^D) will not cause the login shell to exit and log you off the system.
With the history feature you can recall previously executed commands and re-execute them, with
changes if desired.
An alias allows you to use the specified alias name instead of the full command. In the "ls" example
above, typing "ls" will result in "/usr/bin/ls -sbF" being executed. You can tell which "ls" command
is in your path with the built-in which command, i.e.:
which ls
ls: aliased to /usr/bin/ls -sbF
A simple .login could be:
# .login
stty erase ^H # set Control-H to be the erase key
set noglob # prevent wild card pattern matching
eval ‘tset -Q -s -m ’:?xterm’‘ # prompt for the terminal type, assume "xterm"
unset noglob # re-enable wild card pattern matching
Setting and unsetting noglob around tset prevents it from being confused by any csh filename wild card
pattern matching or expansion.
Should you make any changes to your startup files you can initiate the change by sourcing the changed
file. For csh you do this with the built-in source command, i.e.:
source .cshrc
For further information about csh type "man csh" at the shell prompt.

5.5 Job Control

With the C shell, csh, and many newer shells including some newer Bourne shells, you can put jobs
into the background at anytime by appending "&" to the command, as with sh. After submitting a
command you can also do this by typing ^Z (Control-Z) to suspend the job and then "bg" to put it into
the background. To bring it back to the foreground type "fg".
You can have many jobs running in the background. When they are in the background they are no
longer connected to the keyboard for input, but they may still display output to the terminal,
interspersing with whatever else is typed or displayed by your current job. You may want to redirect
I/O to or from files for the job you intend to background. Your keyboard is connected only to the
current, foreground, job.
The built-in jobs command allows you to list your background jobs. You can use the kill command to
kill a background job. With the %n notation you can reference the nth background job with either of
these commands, replacing n with the job number from the output of jobs. So kill the second
background job with "kill %2" and bring the third job to the foreground with "fg %3".

Introduction to Unix  1998 University Technology Services, The Ohio State University 51
 Shells

5.6 History
The C shell, the Korn shell and some other more advanced shells, retain information about the former
commands you’ve executed in the shell. How history is done will depend on the shell used. Here
we’ll describe the C shell history features.

You can use the history and savehist variables to set the number of previously executed commands
to keep track of in this shell and how many to retain between logins, respectively. You could put a
line such as the following in .cshrc to save the last 100 commands in this shell and the last 50 through
the next login.
set history=100 savehist=50
The shell keeps track of the history list and saves it in ~/.history between logins.

You can use the built-in history command to recall previous commands, e.g. to print the last 10:
% history 10
52 cd workshop
53 ls
54 cd unix_intro
55 ls
56 pwd
57 date
58 w
59 alias
60 history
61 history 10

You can repeat the last command by typing !!:

% !!
53 ls
54 cd unix_intro
55 ls
56 pwd
57 date
58 w
59 alias
60 history
61 history 10
62 history 10

52  1998 University Technology Services, The Ohio State University Introduction to Unix
 History

You can repeat any numbered command by prefacing the number with a !, e.g.:
% !57
date
Tue Apr 9 09:55:31 EDT 1996

Or repeat a command starting with any string by prefacing the starting unique part of the string with a
!, e.g.:
% !da
date
Tue Apr 9 09:55:31 EDT 1996

When the shell evaluates the command line it first checks for history substitution before it interprets
anything else. Should you want to use one of these special characters in a shell command you will
need to escape, or quote it first, with a \ before the character, i.e. \!. The history substitution
characters are summarized in the following table.

TABLE 5.1 C Shell History Substitution

Command Substitution Function

!! repeat last command
!n repeat command number n
!-n repeat command n from last
!str repeat command that started with string str
!?str? repeat command with str anywhere on the line
!?str?% select the first argument that had str in it
!: repeat the last command, generally used with a modifier
!:n select the nth argument from the last command (n=0 is the command name)
!:n-m select the nth through mth arguments from the last command
!^ select the first argument from the last command (same as !:1)
!$ select the last argument from the last command
!* select all arguments to the previous command
!:n* select the nth through last arguments from the previous command
!:n- select the nth through next to last arguments from the previous command
^str1^str2^ replace str1 with str2 in its first occurrence in the previous command
!n:s/str1/str2/ substitute str1 with str2 in its first occurrence in the nth command, ending with a g
substitute globally

Additional editing modifiers are described in the man page.

Introduction to Unix  1998 University Technology Services, The Ohio State University 53
 Shells

5.7 Changing your Shell

To change your shell you can usually use the "chsh" or "passwd -e" commands. The option flag, here
-e, may vary from system to system (-s on BSD based systems), so check the man page on your system
for proper usage. Sometimes this feature is disabled. If you can’t change your shell check with your
System Administrator.
The new shell must be the full path name for a valid shell on the system. Which shells are available
to you will vary from system to system. The full path name of a shell may also vary. Normally,
though, the Bourne and C shells are standard, and available as:
/bin/sh
/bin/csh
Some systems will also have the Korn shell standard, normally as:
/bin/ksh
Some shells that are quite popular, but not normally distributed by the OS vendors are bash and tcsh.
These might be placed in /bin or a locally defined directory, e.g. /usr/local/bin or /opt/local/bin. Should
you choose a shell not standard to the OS make sure that this shell, and all login shells available on the
system, are listed in the file /etc/shells. If this file exists and your shell is not listed in this file the file
transfer protocol daemon, ftpd, will not let you connect to this machine. If this file does not exist only
accounts with "standard" shells are allowed to connect via ftp.
You can always try out a shell before you set it as your default shell. To do this just type in the shell
name as you would any other command.

54  1998 University Technology Services, The Ohio State University Introduction to Unix
 File Descriptors

CHAPTER 6 Special Unix Features

One of the most important contributions Unix has made to Operating Systems is the provision of
many utilities for doing common tasks or obtaining desired information. Another is the standard way
in which data is stored and transmitted in Unix systems. This allows data to be transmitted to a file,
the terminal screen, or a program, or from a file, the keyboard, or a program; always in a uniform
manner. The standardized handling of data supports two important features of Unix utilities: I/O
redirection and piping.

With output redirection, the output of a command is redirected to a file rather than to the terminal
screen. With input redirection, the input to a command is given via a file rather than the keyboard.
Other tricks are possible with input and output redirection as well, as you will see. With piping, the
output of a command can be used as input (piped) to a subsequent command. In this chapter we discuss
many of the features and utilities available to Unix users.

6.1 File Descriptors

There are 3 standard file descriptors:

• stdin 0 Standard input to the program

• stdout 1 Standard output from the program
• stderr 2 Standard error output from the program

Normally input is from the keyboard or a file. Output, both stdout and stderr, normally go to the
terminal, but you can redirect one or both of these to one or more files.

You can also specify additional file descriptors, designating them by a number 3 through 9, and
redirect I/O through them.

6.2 File Redirection

Output redirection takes the output of a command and places it into a named file. Input redirection
reads the file as input to the command. The following table summarizes the redirection options.

Introduction to Unix  1998 University Technology Services, The Ohio State University 55
 Special Unix Features

TABLE 6.1 File Redirection

Symbol Redirection
> output redirect
>! same as above, but overrides noclobber option of csh
>> append output
>>! same as above, but overrides noclobber option on csh and creates the file if
it doesn’t already exist.
| pipe output to another command
< input redirection
<<String read from standard input until "String" is encountered as the only thing on the line.
Also known as a "here document" (see Chapter 8).
<<\String same as above, but don’t allow shell substitutions
An example of output redirection is:
cat file1 file2 > file3
The above command concatenates file1 then file2 and redirects (sends) the output to file3. If file3
doesn't already exist it is created. If it does exist it will either be truncated to zero length before the
new contents are inserted, or the command will be rejected, if the noclobber option of the csh is set.
(See the csh in Chapter 4). The original files, file1 and file2, remain intact as separate entities.
Output is appended to a file in the form:
cat file1 >> file2
This command appends the contents of file1 to the end of what already exists in file2. (Does not
overwrite file2).
Input is redirected from a file in the form:
program < file
This command takes the input for program from file.
To pipe output to another command use the form:
command | command

This command makes the output of the first command the input of the second command.

6.2.1 Csh
>& file redirect stdout and stderr to file
>>& append stdout and stderr to file
|& command pipe stdout and stderr to command

To redirect stdout and stderr to two separate files you need to first redirect stdout in a sub-shell, as in:
% (command > out_file) >& err_file

56  1998 University Technology Services, The Ohio State University Introduction to Unix
 File Redirection

6.2.2 Sh
2> file direct stderr to file
> file 2>&1 direct both stdout and stderr to file
>> file 2>&1 append both stdout and stderr to file
2>&1 | command pipe stdout and stderr to command

To redirect stdout and stderr to two separate files you can do:
$ command 1> out_file 2> err_file

or, since the redirection defaults to stdout:

$ command > out_file 2> err_file

With the Bourne shell you can specify other file descriptors (3 through 9) and redirect output through
them. This is done with the form:
n>&m redirect file descriptor n to file descriptor m

We used the above to send stderr (2) to the same place as stdout (1), 2>&1, when we wanted to have
error messages and normal messages to go to file instead of the terminal. If we wanted only the error
messages to go to the file we could do this by using a place holder file descriptor, 3. We’ll first
redirect 3 to 2, then redirect 2 to 1, and finally, we’ll redirect 1 to 3:
$ (command 3>&2 2>&1 1>&3) > file

This sends stderr to 3 then to 1, and stdout to 3, which is redirected to 2. So, in effect, we’ve reversed
file descriptors 1 and 2 from their normal meaning. We might use this in the following example:
$ (cat file 3>&2 2>&1 1>&3) > errfile

So if file is read the information is discarded from the command output, but if file can’t be read the
error message is put in errfile for your later use.

You can close file descriptors when you’re done with them:
m<&- closes an input file descriptor
<&- closes stdin
m>&- closes an output file descriptor
>&- closes stdout

Introduction to Unix  1998 University Technology Services, The Ohio State University 57
 Special Unix Features

6.3 Other Special Command Symbols

In addition to file redirection symbols there are a number of other special symbols you can use on a
command line. These include:
; command separator
& run the command in the background
&& run the command following this only if the previous command completes
successfully, e.g.:
grep string file && cat file
|| run the command following only if the previous command did not complete
successfully, e.g.:
grep string file || echo "String not found."
() the commands within the parentheses are executed in a subshell. The output
of the subshell can be manipulated as above.
’’ literal quotation marks. Don’t allow any special meaning to any characters
within these quotations.
\ escape the following character (take it literally)
"" regular quotation marks. Allow variable and command substitution with
theses quotations (does not disable $ and \ within the string).
‘command‘ take the output of this command and substitute it as an argument(s) on the
command line
# everything following until <newline> is a comment

The \ character can also be used to escape the <newline> character so that you can continue a long
command on more than one physical line of text.

6.4 Wild Cards

The shell and some text processing programs will allow meta-characters, or wild cards, and replace
them with pattern matches. For filenames these meta-characters and their uses are:
? match any single character at the indicated position
* match any string of zero or more characters
[abc...] match any of the enclosed characters
[a-e] match any characters in the range a,b,c,d,e
[!def] match any characters not one of the enclosed characters, sh only
{abc,bcd,cde} match any set of characters separated by comma (,) (no spaces), csh only
~ home directory of the current user, csh only
~user home directory of the specified user, csh only

58  1998 University Technology Services, The Ohio State University Introduction to Unix
 Regular Expression Syntax

CHAPTER 7 Text Processing

7.1 Regular Expression Syntax

Some text processing programs, such as grep, egrep, sed, awk and vi, let you search on patterns
instead of fixed strings. These text patterns are known as regular expressions. You form a regular
expression by combining normal characters and special characters, also known as meta-characters,
with the rules below. With these regular expressions you can do pattern matching on text data.
Regular expressions come in three different forms:
• Anchors which tie the pattern to a location on the line
• Character sets which match a character at a single position
• Modifiers which specify how many times to repeat the previous expression

Regular expression syntax is as follows. Some programs will accept all of these, others may only
accept some.
. match any single character except <newline>
* match zero or more instances of the single character (or meta-character)
immediately preceding it
[abc] match any of the characters enclosed
[a-d] match any character in the enclosed range
[^exp] match any character not in the following expression
^abc the regular expression must start at the beginning of the line (Anchor)
abc$ the regular expression must end at the end of the line (Anchor)
\ treat the next character literally. This is normally used to escape the meaning
of special characters such as "." and "*".
\{n,m\} match the regular expression preceding this a minimum number of n times
and a maximum of m times (0 through 255 are allowed for n and m). The \{
and \} sets should be thought of as single operators. In this case the \
preceding the bracket does not escape its special meaning, but rather turns on
a new one.
\<abc\> will match the enclosed regular expression as long as it is a separate word.
Word boundaries are defined as beginning with a <newline> or anything
except a letter, digit or underscore (_) or ending with the same or a end-of-line
character. Again the \< and \> sets should be thought of as single operators.

Introduction to Unix  1998 University Technology Services, The Ohio State University 59
 Text Processing

\(abc\) saves the enclosed pattern in a buffer. Up to nine patterns can be saved for
each line. You can reference these latter with the \n character set. Again the
\( and \) sets should be thought of as single operators.
\n where n is between 1 and 9. This matches the nth expression previously
saved for this line. Expressions are numbered starting from the left. The \n
should be thought of as a single operator.
& print the previous search pattern (used in the replacement string)

There are a few meta-characters used only by awk and egrep. These are:
+ match one or more of the preceding expression
? match zero or more of the preceding expression
| separator. Match either the preceding or following expression.
() group the regular expressions within and apply the match to the set.

Some examples of the more commonly used regular expressions are:

regular
expression matches
cat the string cat
.at any occurrence of a letter, followed by at, such as cat, rat, mat, bat, fat, hat
xy*z any occurrence of an x, followed by zero or more y's, followed by a z.
^cat cat at the beginning of the line
cat$ cat at the end of the line
\* any occurrence of an asterisk
[cC]at cat or Cat
[^a-zA-Z] any occurrence of a non-alphabetic character
[0-9]$ any line ending with a number
[A-Z][A-Z]* one or more upper case letters
[A-Z]* zero or more upper case letters (In other words, anything.)

60  1998 University Technology Services, The Ohio State University Introduction to Unix
 Text Processing Commands

7.2 Text Processing Commands

TABLE 7.1 Text Processing Commands

Command/Syntax What it will do

awk/nawk [options] file scan for patterns in a file and process the results
grep/egrep/fgrep [options] 'search string' file search the argument (in this case probably a file) for all occurrences
of the search string, and list them.
sed [options] file stream editor for editing files from a script or from the command line

7.2.1 grep

This section provides an introduction to the use of regular expressions and grep.

The grep utility is used to search for generalized regular expressions occurring in Unix files. Regular
expressions, such as those shown above, are best specified in apostrophes (or single quotes) when
specified in the grep utility. The egrep utility provides searching capability using an extended set of
meta-characters. The syntax of the grep utility, some of the available options, and a few examples are
shown below.

Syntax
grep [options] regexp [file[s]]

Common Options
-i ignore case
-c report only a count of the number of lines containing matches, not the
matches themselves
-v invert the search, displaying only lines that do not match
-n display the line number along with the line on which a match was found
-s work silently, reporting only the final status:
0, for match(es) found
1, for no matches
2, for errors
-l list filenames, but not lines, in which matches were found

Introduction to Unix  1998 University Technology Services, The Ohio State University 61
 Text Processing

Examples

Consider the following file:

{unix prompt 5} cat num.list
1 15 fifteen
2 14 fourteen
3 13 thirteen
4 12 twelve
5 11 eleven
6 10 ten
7 9 nine
8 8 eight
9 7 seven
10 6 six
11 5 five
12 4 four
13 3 three
14 2 two
15 1 one

Here are some grep examples using this file. In the first we’ll search for the number 15:
{unix prompt 6} grep '15' num.list
1 15 fifteen
15 1 one

Now we’ll use the "-c" option to count the number of lines matching the search criterion:
{unix prompt 7} grep -c '15' num.list
2

Here we’ll be a little more general in our search, selecting for all lines containing the character 1
followed by either of 1, 2 or 5:
{unix prompt 8} grep '1[125]' num.list
1 15 fifteen
4 12 twelve
5 11 eleven
11 5 five
12 4 four
15 1 one

62  1998 University Technology Services, The Ohio State University Introduction to Unix
 Text Processing Commands

Now we’ll search for all lines that begin with a space:
{unix prompt 9} grep '^ ' num.list
1 15 fifteen
2 14 fourteen
3 13 thirteen
4 12 twelve
5 11 eleven
6 10 ten
7 9 nine
8 8 eight
9 7 seven

Or all lines that don’t begin with a space:

{unix prompt 10} grep '^[^ ]' num.list
10 6 six
11 5 five
12 4 four
13 3 three
14 2 two
15 1 one

The latter could also be done by using the -v option with the original search string, e.g.:
{unix prompt 11} grep -v '^ ' num.list
10 6 six
11 5 five
12 4 four
13 3 three
14 2 two
15 1 one

Here we search for all lines that begin with the characters 1 through 9:
{unix prompt 12} grep '^[1-9]' num.list
10 6 six
11 5 five
12 4 four
13 3 three
14 2 two
15 1 one

Introduction to Unix  1998 University Technology Services, The Ohio State University 63
 Text Processing

This example will search for any instances of t followed by zero or more occurrences of e:
{unix prompt 13} grep 'te*' num.list
1 15 fifteen
2 14 fourteen
3 13 thirteen
4 12 twelve
6 10 ten
8 8 eight
13 3 three
14 2 two

This example will search for any instances of t followed by one or more occurrences of e:
{unix prompt 14} grep 'tee*' num.list
1 15 fifteen
2 14 fourteen
3 13 thirteen
6 10 ten

We can also take our input from a program, rather than a file. Here we report on any lines output by
the who program that begin with the letter l.
{unix prompt 15} who | grep '^l'
lcondron ttyp0 Dec 1 02:41 (lcondron-pc.acs.)

64  1998 University Technology Services, The Ohio State University Introduction to Unix
 Text Processing Commands

7.2.2 sed
The non-interactive, stream editor, sed, edits the input stream, line by line, making the specified
changes, and sends the result to standard output.

Syntax
sed [options] edit_command [file]

The format for the editing commands are:

[address1[,address2]][function][arguments]

where the addresses are optional and can be separated from the function by spaces or tabs. The
function is required. The arguments may be optional or required, depending on the function in use.

Line-number Addresses are decimal line numbers, starting from the first input line and incremented
by one for each. If multiple input files are given the counter continues cumulatively through the files.
The last input line can be specified with the "$" character.

Context Addresses are the regular expression patterns enclosed in slashes (/).

Commands can have 0, 1, or 2 comma-separated addresses with the following affects:

# of addresses lines affected
0 every line of input
1 only lines matching the address
2 first line matching the first address and all lines until, and including, the line
matching the second address. The process is then repeated on subsequent
lines.

Substitution functions allow context searches and are specified in the form:
s/regular_expression_pattern/replacement_string/flag

and should be quoted with single quotes (’) if additional options or functions are specified. These
patterns are identical to context addresses, except that while they are normally enclosed in slashes (/),
any normal character is allowed to function as the delimiter, other than <space> and <newline>.
The replacement string is not a regular expression pattern; characters do not have special meanings
here, except:
& substitute the string specified by regular_expression_pattern
\n substitute the nth string matched by regular_expression_pattern enclosed in
’\(’, ’\)’ pairs.

These special characters can be escaped with a backslash (\) to remove their special meaning.

Introduction to Unix  1998 University Technology Services, The Ohio State University 65
 Text Processing

Common Options
-e script edit script
-n don’t print the default output, but only those lines specified by p or s///p
functions
-f script_file take the edit scripts from the file, script_file

Valid flags on the substitution functions include:

d delete the pattern
g globally substitute the pattern
p print the line

Examples

This example changes all incidents of a comma (,) into a comma followed by a space (, ) when doing
output:
% cat filey | sed s/,/,\ /g

The following example removes all incidents of Jr preceded by a space ( Jr) in filey:
% cat filey | sed s/\ Jr//g

To perform multiple operations on the input precede each operation with the -e (edit) option and
quote the strings. For example, to filter for lines containing "Date: " and "From: " and replace these
without the colon (:), try:
sed -e ’s/Date: /Date /’ -e ’s/From: /From /’

To print only those lines of the file from the one beginning with "Date:" up to, and including, the one
beginning with "Name:" try:
sed -n ’/^Date:/,/^Name:/p’

To print only the first 10 lines of the input (a replacement for head):
sed -n 1,10p

66  1998 University Technology Services, The Ohio State University Introduction to Unix
 Text Processing Commands

7.2.3 awk, nawk, gawk

awk is a pattern scanning and processing language. Its name comes from the last initials of the three
authors: Alfred. V. Aho, Brian. W. Kernighan, and Peter. J. Weinberger. nawk is new awk, a newer
version of the program, and gawk is gnu awk, from the Free Software Foundation. Each version is a
little different. Here we’ll confine ourselves to simple examples which should be the same for all
versions. On some OSs awk is really nawk.

awk searches its input for patterns and performs the specified operation on each line, or fields of the
line, that contain those patterns. You can specify the pattern matching statements for awk either on
the command line, or by putting them in a file and using the -f program_file option.

Syntax
awk program [file]

where program is composed of one or more:

pattern { action }

fields. Each input line is checked for a pattern match with the indicated action being taken on a
match. This continues through the full sequence of patterns, then the next line of input is checked.

Input is divided into records and fields. The default record separator is <newline>, and the variable
NR keeps the record count. The default field separator is whitespace, spaces and tabs, and the
variable NF keeps the field count. Input field, FS, and record, RS, separators can be set at any time to
match any single character. Output field, OFS, and record, ORS, separators can also be changed to
any single character, as desired. $n, where n is an integer, is used to represent the nth field of the
input record, while $0 represents the entire input record.

BEGIN and END are special patterns matching the beginning of input, before the first field is read,
and the end of input, after the last field is read, respectively.

Printing is allowed through the print, and formatted print, printf, statements.

Patterns may be regular expressions, arithmetic relational expressions, string-valued expressions,

and boolean combinations of any of these. For the latter the patterns can be combined with the
boolean operators below, using parentheses to define the combination:
|| or
&& and
! not

Comma separated patterns define the range for which the pattern is applicable, e.g.:
/first/,/last/

selects all lines starting with the one containing first, and continuing inclusively, through the one
containing last.

Introduction to Unix  1998 University Technology Services, The Ohio State University 67
 Text Processing

To select lines 15 through 20 use the pattern range:

NR == 15, NR == 20

Regular expressions must be enclosed with slashes (/) and meta-characters can be escaped with the
backslash (\). Regular expressions can be grouped with the operators:
| or, to separate alternatives
+ one or more
? zero or one

A regular expression match can be either of:

~ contains the expression
!~ does not contain the expression

So the program:
$1 ~ /[Ff]rank/

is true if the first field, $1, contains "Frank" or "frank" anywhere within the field. To match a field
identical to "Frank" or "frank" use:
$1 ~ /^[Ff]rank$/

Relational expressions are allowed using the relational operators:

< less than
<= less than or equal to
== equal to
>= greater than or equal to
!= not equal to
> greater than

Offhand you don’t know if variables are strings or numbers. If neither operand is known to be
numeric, than string comparisons are performed. Otherwise, a numeric comparison is done. In the
absence of any information to the contrary, a string comparison is done, so that:
$1 > $2

will compare the string values. To ensure a numerical comparison do something similar to:
( $1 + 0 ) > $2

The mathematical functions: exp, log and sqrt are built-in.

68  1998 University Technology Services, The Ohio State University Introduction to Unix
 Text Processing Commands

Some other built-in functions include:

index(s,t) returns the position of string s where t first occurs, or 0 if it doesn’t
length(s) returns the length of string s
substr(s,m,n) returns the n-character substring of s, beginning at position m

Arrays are declared automatically when they are used, e.g.:

arr[i] = $1

assigns the first field of the current input record to the ith element of the array.

Flow control statements using if-else, while, and for are allowed with C type syntax:
for (i=1; i <= NF; i++) {actions}
while (i<=NF) {actions}
if (i<NF) {actions}

Common Options
-f program_file read the commands from program_file
-Fc use character c as the field separator character

Examples
% cat filex | tr a-z A-Z | awk -F: '{printf ("7R %-6s %-9s %-24s \n",$1,$2,$3)}'>upload.file

cats filex, which is formatted as follows:

nfb791:99999999:smith
7ax791:999999999:jones
8ab792:99999999:chen
8aa791:999999999:mcnulty

changes all lower case characters to upper case with the tr utility, and formats the file into the
following which is written into the file upload.file:
7R NFB791 99999999 SMITH
7R 7AX791 999999999 JONES
7R 8AB792 99999999 CHEN
7R 8AA791 999999999 MCNULTY

Introduction to Unix  1998 University Technology Services, The Ohio State University 69
 Other Useful Commands

CHA P TE R 8 Other Useful Commands

8.1 Working With Files

This section will describe a number of commands that you might find useful in examining and
manipulating the contents of your files.

TABLE 8.1 File utilities

Command/Syntax What it will do

cmp [options] file1 file2 compare two files and list where differences occur (text or binary files)
cut [options] [file(s)] cut specified field(s)/character(s) from lines in file(s)
diff [options] file1 file2 compare the two files and display the differences (text files only)
file [options] file classify the file type
find directory [options] [actions] find files matching a type or pattern
ln [options] source_file target link the source_file to the target
paste [options] file paste field(s) onto the lines in file
sort [options] file sort the lines of the file according to the options chosen
strings [options] file report any sequence of 4 or more printable characters ending in <NL> or
<NULL>. Usually used to search binary files for ASCII strings.
tee [options] file copy stdout to one or more files
touch [options] [date] file create an empty file, or update the access time of an existing file
tr [options] string1 string2 translate the characters in string1 from stdin into those in string2 in stdout
uniq [options] file remove repeated lines in a file
wc [options] [file(s)] display word (or character or line) count for file(s)

70  1998 University Technology Services, The Ohio State University Introduction to Unix
 Working With Files

8.1.1 cmp - compare file contents

The cmp command compares two files, and (without options) reports the location of the first
difference between them. It can deal with both binary and ASCII file comparisons. It does a
byte-by-byte comparison.

Syntax
cmp [options] file1 file2 [skip1] [skip2]

The skip numbers are the number of bytes to skip in each file before starting the comparison.

Common Options
-l report on each difference
-s report exit status only, not byte differences

Examples

Given the files mon.logins:and tues.logins:

ageorge ageorge
bsmith cbetts
cbetts jchen
jchen jdoe
jmarsch jmarsch
lkeres lkeres
mschmidt proy
sphillip sphillip
wyepp wyepp

The comparison of the two files yields:

% cmp mon.logins tues.logins
mon.logins tues.logins differ: char 9, line 2

The default it to report only the first difference found.

This command is useful in determining which version of a file should be kept when there is more than
one version.

Introduction to Unix  1998 University Technology Services, The Ohio State University 71
 Other Useful Commands

8.1.2 diff - differences in files

The diff command compares two files, directories, etc, and reports all differences between the two. It
deals only with ASCII files. It’s output format is designed to report the changes necessary to convert
the first file into the second.

Syntax
diff [options] file1 file2

Common Options
-b ignore trailing blanks
-i ignore the case of letters
-w ignore <space> and <tab> characters
-e produce an output formatted for use with the editor, ed
-r apply diff recursively through common sub-directories

Examples

For the mon.logins and tues.logins files above, the difference between them is given by:
% diff mon.logins tues.logins
2d1
< bsmith
4a4
> jdoe
7c7
< mschmidt
---
> proy

Note that the output lists the differences as well as in which file the difference exists. Lines in the
first file are preceded by "< ", and those in the second file are preceded by "> ".

72  1998 University Technology Services, The Ohio State University Introduction to Unix
 Working With Files

8.1.3 cut - select parts of a line

The cut command allows a portion of a file to be extracted for another use.

Syntax
cut [options] file

Common Options
-c character_list character positions to select (first character is 1)
-d delimiter field delimiter (defaults to <TAB>)
-f field_list fields to select (first field is 1)

Both the character and field lists may contain comma-separated or blank-character-separated
numbers (in increasing order), and may contain a hyphen (-) to indicate a range. Any numbers
missing at either before (e.g. -5) or after (e.g. 5-) the hyphen indicates the full range starting with the
first, or ending with the last character or field, respectively. Blank-character-separated lists must be
enclosed in quotes. The field delimiter should be enclosed in quotes if it has special meaning to the
shell, e.g. when specifying a <space> or <TAB> character.

Examples

In these examples we will use the file users:

jdoe John Doe 4/15/96
lsmith Laura Smith 3/12/96
pchen Paul Chen 1/5/96
jhsu Jake Hsu 4/17/96
sphilip Sue Phillip 4/2/96

If you only wanted the username and the user's real name, the cut command could be used to get only
that information:
% cut -f 1,2 users
jdoe John Doe
lsmith Laura Smith
pchen Paul Chen
jhsu Jake Hsu
sphilip Sue Phillip

Introduction to Unix  1998 University Technology Services, The Ohio State University 73
 Other Useful Commands

The cut command can also be used with other options. The -c option allows characters to be the
selected cut. To select the first 4 characters:
% cut -c 1-4 users

This yields:
jdoe
lsmi
pche
jhsu
sphi

thus cutting out only the first 4 characters of each line.

8.1.4 paste - merge files

The paste command allows two files to be combined side-by-side. The default delimiter between the
columns in a paste is a tab, but options allow other delimiters to be used.

Syntax
paste [options] file1 file2

Common Options
-d list list of delimiting characters
-s concatenate lines

The list of delimiters may include a single character such as a comma; a quoted string, such as a
space; or any of the following escape sequences:
\n <newline> character
\t <tab> character
\\ backslash character
\0 empty string (non-null character)

It may be necessary to quote delimiters with special meaning to the shell.

A hyphen (-) in place of a file name is used to indicate that field should come from standard input.

74  1998 University Technology Services, The Ohio State University Introduction to Unix
 Working With Files

Examples

Given the file users:

jdoe John Doe 4/15/96
lsmith Laura Smith 3/12/96
pchen Paul Chen 1/5/96
jhsu Jake Hsu 4/17/96
sphilip Sue Phillip 4/2/96

and the file phone:

John Doe 555-6634
Laura Smith 555-3382
Paul Chen 555-0987
Jake Hsu 555-1235
Sue Phillip 555-7623

the paste command can be used in conjunction with the cut command to create a new file, listing, that
includes the username, real name, last login, and phone number of all the users. First, extract the
phone numbers into a temporary file, temp.file:
% cut -f2 phone > temp.file
555-6634
555-3382
555-0987
555-1235
555-7623

The result can then be pasted to the end of each line in users and directed to the new file, listing:
% paste users temp.file > listing
jdoe John Doe 4/15/96 237-6634
lsmith Laura Smith 3/12/96 878-3382
pchen Paul Chen 1/5/96 888-0987
jhsu Jake Hsu 4/17/96 545-1235
sphilip Sue Phillip 4/2/96 656-7623

This could also have been done on one line without the temporary file as:
% cut -f2 phone | paste users - > listing

with the same results. In this case the hyphen (-) is acting as a placeholder for an input field (namely,
the output of the cut command).

Introduction to Unix  1998 University Technology Services, The Ohio State University 75
 Other Useful Commands

8.1.5 touch - create a file

The touch command can be used to create a new (empty) file or to update the last access date/time on
an existing file. The command is used primarily when a script requires the pre-existence of a file (for
example, to which to append information) or when the script is checking for last date or time a
function was performed.

Syntax
touch [options] [date_time] file
touch [options] [-t time] file

Common Options
-a change the access time of the file (SVR4 only)
-c don’t create the file if it doesn’t already exist
-f force the touch, regardless of read/write permissions
-m change the modification time of the file (SVR4 only)
-t time use the time specified, not the current time (SVR4 only)

When setting the "-t time" option it should be in the form:

[[CC]YY]MMDDhhmm[.SS]

where:
CC first two digits of the year
YY second two digits of the year
MM month, 01-12
DD day of month, 01-31
hh hour of day, 00-23
mm minute, 00-59
SS second, 00-61

The date_time options has the form:

MMDDhhmm[YY]

where these have the same meanings as above.

The date cannot be set to be before 1969 or after January 18, 2038.

Examples

To create a file:
% touch filename

76  1998 University Technology Services, The Ohio State University Introduction to Unix
 Working With Files

8.1.6 wc - count words in a file

wc stands for "word count"; the command can be used to count the number of lines, characters, or
words in a file.

Syntax
wc [options] file

Common Options
-c count bytes
-m count characters (SVR4)
-l count lines
-w count words

If no options are specified it defaults to "-lwc".

Examples

Given the file users:

jdoe John Doe 4/15/96
lsmith Laura Smith 3/12/96
pchen Paul Chen 1/5/96
jhsu Jake Hsu 4/17/96
sphilip Sue Phillip 4/2/96

the result of using a wc command is as follows:

% wc users
5 20 121 users

The first number indicates the number of lines in the file, the second number indicates the number of
words in the file, and the third number indicates the number of characters.

Using the wc command with one of the options (-l, lines; -w, words; or -c, characters) would result in
only one of the above. For example, "wc -l users" yields the following result:

5 users

Introduction to Unix  1998 University Technology Services, The Ohio State University 77
 Other Useful Commands

8.1.7 ln - link to another file

The ln command creates a "link" or an additional way to access (or gives an additional name to)
another file.

Syntax
ln [options] source [target]

If not specified target defaults to a file of the same name in the present working directory.

Common Options
-f force a link regardless of target permissions; don’t report errors (SVR4 only)
-s make a symbolic link

Examples

A symbolic link is used to create a new path to another file or directory. If a group of users, for
example, is accustomed to using a command called chkmag, but the command has been rewritten and
is now called chkit, creating a symbolic link so the users will automatically execute chkit when they
enter the command chkmag will ease transition to the new command.

A symbolic link would be done in the following way:

% ln -s chkit chkmag

The long listing for these two files is now as follows:

16 -rwxr-x--- 1 lindadb acs 15927 Apr 23 04:10 chkit
1 lrwxrwxrwx 1 lindadb acs 5 Apr 23 04:11 chkmag -> chkit

Note that while the permissions for chkmag are open to all, since it is linked to chkit, the permissions,
group and owner characteristics for chkit will be enforced when chkmag is run.

With a symbolic link, the link can exist without the file or directory it is linked to existing first.

A hard link can only be done to another file on the same file system, but not to a directory (except by
the superuser). A hard link creates a new directory entry pointing to the same inode as the original
file. The file linked to must exist before the hard link can be created. The file will not be deleted until
all the hard links to it are removed. To link the two files above with a hard link to each other do:
% ln chkit chkmag

Then a long listing shows that the inode number (742) is the same for each:
% ls -il chkit chkmag
742 -rwxr-x--- 2 lindadb acs 15927 Apr 23 04:10 chkit
742 -rwxr-x--- 2 lindadb acs 15927 Apr 23 04:10 chkmag

78  1998 University Technology Services, The Ohio State University Introduction to Unix
 Working With Files

8.1.8 sort - sort file contents

The sort command is used to order the lines of a file. Various options can be used to choose the order
as well as the field on which a file is sorted. Without any options, the sort compares entire lines in the
file and outputs them in ASCII order (numbers first, upper case letters, then lower case letters).

Syntax
sort [options] [+pos1 [ -pos2 ]] file

Common Options
-b ignore leading blanks (<space> & <tab>) when determining starting and
ending characters for the sort key
-d dictionary order, only letters, digits, <space> and <tab> are significant
-f fold upper case to lower case
-k keydef sort on the defined keys (not available on all systems)
-i ignore non-printable characters
-n numeric sort
-o outfile output file
-r reverse the sort
-t char use char as the field separator character
-u unique; omit multiple copies of the same line (after the sort)
+pos1 [-pos2] (old style) provides functionality similar to the "-k keydef" option.

For the +/-position entries pos1 is the starting word number, beginning with 0 and pos2 is the ending
word number. When -pos2 is omitted the sort field continues through the end of the line. Both pos1
and pos2 can be written in the form w.c, where w is the word number and c is the character within the
word. For c 0 specifies the delimiter preceding the first character, and 1 is the first character of the
word. These entries can be followed by type modifiers, e.g. n for numeric, b to skip blanks, etc.

The keydef field of the "-k" option has the syntax:

start_field [type] [ ,end_field [type] ]

where:
start_field, end_field define the keys to restrict the sort to a portion of the line
type modifies the sort, valid modifiers are given the single characters (bdfiMnr)
from the similar sort options, e.g. a type b is equivalent to "-b", but applies
only to the specified field

Introduction to Unix  1998 University Technology Services, The Ohio State University 79
 Other Useful Commands

Examples

In the file users:

jdoe John Doe 4/15/96
lsmith Laura Smith 3/12/96
pchen Paul Chen 1/5/96
jhsu Jake Hsu 4/17/96
sphilip Sue Phillip 4/2/96

sort users yields the following:

jdoe John Doe 4/15/96
jhsu Jake Hsu 4/17/96
lsmith Laura Smith 3/12/96
pchen Paul Chen 1/5/96
sphilip Sue Phillip 4/2/96

If, however, a listing sorted by last name is desired, use the option to specify which field to sort on
(fields are numbered starting at 0):
% sort +2 users:
pchen Paul Chen 1/5/96
jdoe John Doe 4/15/96
jhsu Jake Hsu 4/17/96
sphilip Sue Phillip 4/2/96
lsmith Laura Smith 3/12/96

To sort in reverse order:

% sort -r users:
sphilip Sue Phillip 4/2/96
pchen Paul Chen 1/5/96
lsmith Laura Smith 3/12/96
jhsu Jake Hsu 4/17/96
jdoe John Doe 4/15/96

80  1998 University Technology Services, The Ohio State University Introduction to Unix
 Working With Files

A particularly useful sort option is the -u option, which eliminates any duplicate entries in a file while
ordering the file. For example, the file todays.logins:
sphillip
jchen
jdoe
lkeres
jmarsch
ageorge
lkeres
proy
jchen

shows a listing of each username that logged into the system today. If we want to know how many
unique users logged into the system today, using sort with the -u option will list each user only once.
(The command can then be piped into "wc -l" to get a number):
% sort -u todays.logins
ageorge
jchen
jdoe
jmarsch
lkeres
proy
sphillip

Introduction to Unix  1998 University Technology Services, The Ohio State University 81
 Other Useful Commands

8.1.9 tee - copy command output

tee sends standard in to specified files and also to standard out. It’s often used in command pipelines.

Syntax
tee [options] [file[s]]

Common Options
-a append the output to the files
-i ignore interrupts

Examples

In this first example the output of who is displayed on the screen and stored in the file users.file:
brigadier: condron [55]> who | tee users.file
condron ttyp0 Apr 22 14:10 (lcondron-pc.acs.)
frank ttyp1 Apr 22 16:19 (nyssa)
condron ttyp9 Apr 22 15:52 (lcondron-mac.acs)

brigadier: condron [56]> cat users.file

condron ttyp0 Apr 22 14:10 (lcondron-pc.acs.)
frank ttyp1 Apr 22 16:19 (nyssa)
condron ttyp9 Apr 22 15:52 (lcondron-mac.acs)

In this next example the output of who is sent to the files users.a and users.b. It is also piped to the
wc command, which reports the line count.
brigadier: condron [57]> who | tee users.a users.b | wc -l
3

brigadier: condron [58]> cat users.a

condron ttyp0 Apr 22 14:10 (lcondron-pc.acs.)
frank ttyp1 Apr 22 16:19 (nyssa)
condron ttyp9 Apr 22 15:52 (lcondron-mac.acs)

brigadier: condron [59]> cat users.b

condron ttyp0 Apr 22 14:10 (lcondron-pc.acs.)
frank ttyp1 Apr 22 16:19 (nyssa)
condron ttyp9 Apr 22 15:52 (lcondron-mac.acs)

82  1998 University Technology Services, The Ohio State University Introduction to Unix
 Working With Files

In the following example a long directory listing is sent to the file files.long. It is also piped to the
grep command which reports which files were last modified in August.
brigadier: condron [60]> ls -l | tee files.long |grep Aug
1 drwxr-sr-x 2 condron 512 Aug 8 1995 News/
2 -rw-r--r-- 1 condron 1076 Aug 8 1995 magnus.cshrc
2 -rw-r--r-- 1 condron 1252 Aug 8 1995 magnus.login
brigadier: condron [63]> cat files.long
total 34
2 -rw-r--r-- 1 condron 1253 Oct 10 1995 #.login#
1 drwx------ 2 condron 512 Oct 17 1995 Mail/
1 drwxr-sr-x 2 condron 512 Aug 8 1995 News/
5 -rw-r--r-- 1 condron 4299 Apr 21 00:18 editors.txt
2 -rw-r--r-- 1 condron 1076 Aug 8 1995 magnus.cshrc
2 -rw-r--r-- 1 condron 1252 Aug 8 1995 magnus.login
7 -rw-r--r-- 1 condron 6436 Apr 21 23:50 resources.txt
4 -rw-r--r-- 1 condron 3094 Apr 18 18:24 telnet.ftp
1 drwxr-sr-x 2 condron 512 Apr 21 23:56 uc/
1 -rw-r--r-- 1 condron 1002 Apr 22 00:14 uniq.tee.txt
1 -rw-r--r-- 1 condron 1001 Apr 20 15:05 uniq.tee.txt~
7 -rw-r--r-- 1 condron 6194 Apr 15 20:18 unixgrep.txt

Introduction to Unix  1998 University Technology Services, The Ohio State University 83
 Other Useful Commands

8.1.10 uniq - remove duplicate lines

uniq filters duplicate adjacent lines from a file.

Syntax
uniq [options] [+|-n] file [file.new]

Common Options
-d one copy of only the repeated lines
-u select only the lines not repeated
+n ignore the first n characters
-s n same as above (SVR4 only)
-n skip the first n fields, including any blanks (<space> & <tab>)
-f fields same as above (SVR4 only)

Examples

Consider the following file and example, in which uniq removes the 4th line from file and places the
result in a file called file.new.
{unix prompt 1} cat file
1236
4536
7890
7890
{unix prompt 2} uniq file file.new
{unix prompt 3} cat file.new
1236
4536
7890

Below, the -n option of the uniq command is used to skip the first 2 fields in file, and filter out lines
which are duplicates from the 3rd field onward.
{unix prompt 4} uniq -2 file
1236
7890

84  1998 University Technology Services, The Ohio State University Introduction to Unix
 Working With Files

8.1.11 strings - find ASCII strings

To search a binary file for printable, ASCII, strings use the strings command. It searches for any
sequence of 4 or more ASCII characters terminated by a <newline> or null character. I find this
command useful for searching for file names and possible error messages within compiled programs
that I don’t have source code for.

Syntax
strings [options] file

Common Options
-n number use number as the minimum string length, rather than 4 (SVR4 only)
-number same as above
-t format precede the string with the byte offset from the start of the file, where format
is one of: d = decimal, o = octal, x = hexadecimal (SVR4 only)
-o precede the string with the byte offset in decimal (BSD only)

Examples
% strings /bin/cut
SUNW_OST_OSCMD
no delimiter specified
invalid delimiter
b:c:d:f:ns
cut: -n may only be used with -b
cut: -d may only be used with -f
cut: -s may only be used with -f
no list specified
cut: cannot open %s
invalid range specifier
too many ranges specified
ranges must be increasing
invalid character in range
Internal error processing input
invalid multibyte character
unable to allocate enough memory
unable to allocate enough memory
cut:
usage: cut -b list [-n] [filename ...]
cut -c list [filename ...]
cut -f list [-d delim] [-s] [filename]

Introduction to Unix  1998 University Technology Services, The Ohio State University 85
 Other Useful Commands

8.1.12 file - file type

This program, file, examines the selected file and tries to determine what type of file it is. It does this
by reading the first few bytes of the file and comparing them with the table in /etc/magic. It can
determine ASCII text files, tar formatted files, compressed files, etc.

Syntax
file [options] [-m magic_file] [-f file_list] file

Common Options
-c check the magic file for errors in format
-f file_list file_list contains a list of files to examine
-h don’t follow symbolic links (SVR4 only)
-L follow symbolic links (BSD only)
-m magic_file use magic_file as the magic file instead of /etc/magic

Examples

Below we list the output from the command "file filename" for some representative files.
/etc/magic: ascii text
/usr/local/bin/gzip: Sun demand paged SPARC executable dynamically linked
/usr/bin/cut: ELF 32-bit MSB executable SPARC Version 1, dynamically linked, stripped
source.tar: USTAR tar archive
source.tar.Z: compressed data block compressed 16 bits

8.1.13 tr - translate characters

The tr command translates characters from stdin to stdout.

Syntax
tr [options] string1 [string2]

With no options the characters in string1 are translated into the characters in string2, character by
character in the string arrays. The first character in string1 is translated into the first character in
string2, etc.

A range of characters in a string is specified with a hyphen between the upper and lower characters of
the range, e.g. to specify all lower case alphabetic characters use ’[a-z]’.

Repeated characters in string2 can be represented with the ’[x*n]’ notation, where character x is
repeated n times. If n is 0 or absent it is assumed to be as large as needed to match string1.

86  1998 University Technology Services, The Ohio State University Introduction to Unix
 Working With Files

Characters can include \octal (BSD and SVR4) and \character (SVR4 only) notation. Here "octal"
is replaced by the one, two, or three octal integer sequence encoding the ASCII character and
"character" can be one of:
b back space
f form feed
n new line
r carriage return
t tab
v vertical tab

The SVR4 version of tr allows the operand ":class:" in the string field where class can take on
character classification values, including:
alpha alphabetic characters
lower lower case alphabetic characters
upper upper case alphabetic characters

Common Options
-c complement the character set in string1
-d delete the characters in string1
-s squeeze a string of repeated characters in string1 to a single character

Examples

The following examples will use as input the file, a list of P. G. Wodehouse Jeeves & Wooster books.
The Inimitable Jeeves [1923] The Mating Season [1949]
Carry On, Jeeves [1925] Ring for Jeeves [1953]
Very Good, Jeeves [1930] Jeeves and the Feudal Spirit [1954]
Thank You, Jeeves [1934] Jeeves in the Offing [1960]
Right Ho, Jeeves [1934] Stiff Upper Lip, Jeeves [1963]
The Code of the Woosters [1938] Much Obliged, Jeeves [1971]
Joy in the Morning [1946] Aunts Aren't Gentlemen [1974]

To translate all lower case alphabetic characters to upper case we could use either of:
tr ’[a-z]’ ’[A-Z]’ or tr ’[:lower:]’ ’[:upper:]’

Introduction to Unix  1998 University Technology Services, The Ohio State University 87
 Other Useful Commands

Since tr reads from stdin we first cat the file and pipe the output to tr, as in:
% cat wodehouse | tr ’[a-z]’ ’[A-Z]’
THE INIMITABLE JEEVES [1923] THE MATING SEASON [1949]
CARRY ON, JEEVES [1925] RING FOR JEEVES [1953]
VERY GOOD, JEEVES [1930] JEEVES AND THE FEUDAL SPIRIT [1954]
THANK YOU, JEEVES [1934] JEEVES IN THE OFFING [1960]
RIGHT HO, JEEVES [1934] STIFF UPPER LIP, JEEVES [1963]
THE CODE OF THE WOOSTERS [1938] MUCH OBLIGED, JEEVES [1971]
JOY IN THE MORNING [1946] AUNTS AREN'T GENTLEMEN [1974]

We could delete all numbers with:

% cat wodehouse | tr -d ’[0-9]’
The Inimitable Jeeves [] The Mating Season []
Carry On, Jeeves [] Ring for Jeeves []
Very Good, Jeeves [] Jeeves and the Feudal Spirit []
Thank You, Jeeves [] Jeeves in the Offing []
Right Ho, Jeeves [] Stiff Upper Lip, Jeeves []
The Code of the Woosters [] Much Obliged, Jeeves []
Joy in the Morning [] Aunts Aren't Gentlemen []

To squeeze all multiple occurrences of the characters e, r, and f:

% cat wodehouse | tr -s ’erf’
The Inimitable Jeves [1923] The Mating Season [1949]
Cary On, Jeves [1925] Ring for Jeves [1953]
Very Good, Jeves [1930] Jeves and the Feudal Spirit [1954]
Thank You, Jeves [1934] Jeves in the Ofing [1960]
Right Ho, Jeves [1934] Stif Upper Lip, Jeves [1963]
The Code of the Woosters [1938] Much Obliged, Jeves [1971]
Joy in the Morning [1946] Aunts Aren't Gentlemen [1974]

88  1998 University Technology Services, The Ohio State University Introduction to Unix
 Working With Files

8.1.14 find - find files

The find command will recursively search the indicated directory tree to find files matching a type or
pattern you specify. find can then list the files or execute arbitrary commands based on the results.

Syntax
find directory [search options] [actions]

Common Options

For the time search options the notation in days, n is:

+n more than n days
n exactly n days
-n less than n days

Some file characteristics that find can search for are:

time that the file was last accessed or changed
-atime n access time, true if accessed n days ago
-ctime n change time, true if the files status was changed n days ago
-mtime n modified time, true if the files data was modified n days ago
-newer filename true if newer than filename
-type type type of file, where type can be:
b block special file
c character special file
d directory
l symbolic link
p named pipe (fifo)
f regular file
-fstype type type of file system, where type can be any valid file system type, e.g.: ufs
(Unix File System) and nfs (Network File System)
-user username true if the file belongs to the user username
-group groupname true if the file belongs to the group groupname
-perm [-]mode permissions on the file, where mode is the octal modes for the chmod
command. When mode is precede by the minus sign only the bits that are set
are compared.
-exec command execute command. The end of command is indicated by and escaped
semicolon (\;). The command argument, {}, replaces the current path name.
-name filename true if the file is named filename. Wildcard pattern matches are allowed if
the meta-character is escaped from the shell with a backslash (\).
-ls always true. It prints a long listing of the current pathname.
-print print the pathnames found (default for SVR4, not for BSD)

Introduction to Unix  1998 University Technology Services, The Ohio State University 89
 Other Useful Commands

Complex expressions are allowed. Expressions should be grouped within parenthesis (escaping the
parenthesis with a backslash to prevent the shell from interpreting them). The exclamation symbol (!)
can be used to negate an expression. The operators: -a (and) and -o (or) are used to group
expressions.

Examples

find will recursively search through sub-directories, but for the purpose of these examples we will
just use the following files:
14 -rw-r--r-- 1 frank staff 6682 Feb 5 10:04 library
6 -r--r----- 1 frank staff 3034 Mar 16 1995 netfile
34 -rw-r--r-- 1 frank staff 17351 Feb 5 10:04 standard
2 -rwxr-xr-x 1 frank staff 386 Apr 26 09:51 tr25*

To find all files newer than the file, library:

% find . -newer library -print
./tr25
./standard

To find all files with general read or execute permission set, and then to change the permissions on
those files to disallow this:
% find . \( -perm -004 -o -perm -001 \) -exec chmod o-rx {} \; -exec ls -al {} \;
-rw-r----- 1 frank staff 6682 Feb 5 10:04 ./library
-rwxr-x--- 1 frank staff 386 Apr 26 09:51 ./tr25
-rw-r----- 1 frank staff 17351 Feb 5 10:04 ./standard

In this example the parentheses and semicolons are escaped with a backslash to prevent the shell from
interpreting them. The curly brackets are automatically replaced by the results from the previous
search and the semicolon ends the command.

We could search for any file name containing the string "ar" with:
% find . -name \*ar\* -ls
326584 7 -rw-r----- 1 frank staff 6682 Feb 5 10:04 ./library
326585 17 -rw-r----- 1 frank staff 17351 Feb 5 10:04 ./standard

where the -ls option prints out a long listing, including the inode numbers.

90  1998 University Technology Services, The Ohio State University Introduction to Unix
 File Archiving, Compression and Conversion

8.2 File Archiving, Compression and

Conversion

TABLE 8.2 File Archiving, Compression and Conversion Commands

Command/Syntax What it will do

compress/uncompress/zcat [options] file[.Z] compress or uncompress a file. Compressed files are stored with a .Z
ending.
dd [if=infile] [of=outfile] [operand=value] copy a file, converting between ASCII and EBCDIC or swapping
byte order, as specified
gzip/gunzip/zcat [options] file[.gz] compress or uncompress a file. Compressed files are stored with a
.gz ending
od [options] file octal dump a binary file, in octal, ASCII, hex, decimal, or character
mode.
tar key[options] [file(s)] tape archiver--refer to man pages for details on creating, listing, and
retrieving from archive files. Tar files can be stored on tape or disk.
uudecode [file] decode a uuencoded file, recreating the original file
uuencode [file] new_name encode binary file to 7-bit ASCII, useful when sending via email, to
be decoded as new_name at destination

8.2.1 File Compression

The compress command is used to reduce the amount of disk space utilized by a file. When a file has
been compressed using the compress command, a suffix of .Z is appended to the file name. The
ownership modes and access and modification times of the original file are preserved. uncompress
restores the files originally compressed by compress.

Syntax
compress [options] [file]
uncompress [options] [file.Z]
zcat [file.Z]

Common Options
-c write to standard output and don’t create or change any files
-f force compression of a file, even if it doesn’t reduce the size of the file or if
the target file (file.Z) already exists.
-v verbose. Report on the percentage reduction for the file.

zcat writes to standard output. It is equivalent to "uncompress -c".

Introduction to Unix  1998 University Technology Services, The Ohio State University 91
 Other Useful Commands

Examples

Given the files:

96 -rw-r--r-- 1 lindadb acs 45452 Apr 24 09:13 logins.beauty
184 -rw-r--r-- 1 lindadb acs 90957 Apr 24 09:13 logins.bottom
152 -rw-r--r-- 1 lindadb acs 75218 Apr 24 09:13 logins.photon
168 -rw-r--r-- 1 lindadb acs 85970 Apr 24 09:13 logins.top

These can be compressed with:

% compress logins.*

which creates the files:

24 -rw-r--r-- 1 lindadb acs 8486 Apr 24 09:13 logins.beauty.Z
40 -rw-r--r-- 1 lindadb acs 16407 Apr 24 09:13 logins.bottom.Z
24 -rw-r--r-- 1 lindadb acs 10909 Apr 24 09:13 logins.photon.Z
32 -rw-r--r-- 1 lindadb acs 16049 Apr 24 09:13 logins.top.Z

The original files are lost.

To display a compressed file, the zcat command is used:

% zcat logins.beauty.Z | head
beauty:01/22/94:#total logins,4338:#different UIDs,2290
beauty:01/23/94:#total logins,1864:#different UIDs,1074
beauty:01/24/94:#total logins,2317:#different UIDs,1242
beauty:01/25/94:#total logins,3673:#different UIDs,2215
beauty:01/26/94:#total logins,3532:#different UIDs,2216
beauty:01/27/94:#total logins,3096:#different UIDs,1984
beauty:01/28/94:#total logins,3724:#different UIDs,2212
beauty:01/29/94:#total logins,3460:#different UIDs,2161
beauty:01/30/94:#total logins,1408:#different UIDs,922
beauty:01/31/94:#total logins,2175:#different UIDs,1194

A display of the file using commands other than zcat yields an unreadable, binary, output.

The uncompress command is used to return the file to its original format:
% uncompress logins.*.Z ; ls -als logins.*
96 -rw-r--r-- 1 lindadb acs 45452 Apr 24 09:13 logins.beauty
184 -rw-r--r-- 1 lindadb acs 90957 Apr 24 09:13 logins.bottom
152 -rw-r--r-- 1 lindadb acs 75218 Apr 24 09:13 logins.photon
168 -rw-r--r-- 1 lindadb acs 85970 Apr 24 09:13 logins.top

92  1998 University Technology Services, The Ohio State University Introduction to Unix
 File Archiving, Compression and Conversion

In addition to the standard Unix compress, uncompress, zcat utilities there are a set of GNU ones
freely available. These do an even better job of compression using a more efficient algorithm. The
GNU programs to provide similar functions to those above are often installed as gzip, gunzip, and
zcat, respectively. Files compressed with gzip are given the endings .z or .gz. GNU software can be
obtained via anonymous ftp from ftp://ftp.gnu.org/pub/gnu.

8.2.2 tar - archive files

The tar command combines files into one device or filename for archiving purposes. The tar
command does not compress the files; it merely makes a large quantity of files more manageable.

Syntax
tar [options] [directory file]

Common Options
c create an archive (begin writting at the start of the file)
t table of contents list
x extract from an archive
v verbose
f archive file name
b archive block size

tar will accept its options either with or without a preceding hyphen (-). The archive file can be a disk
file, a tape device, or standard input/output. The latter are represented by a hyphen.

Examples

Given the files and size indications below:

45 logs.beauty
89 logs.bottom
74 logs.photon
84 logs.top

tar can combine these into one file, logfile.tar:

% tar -cf logfile.tar logs.* ; ls -s logfile.tar
304 logfile.tar

Many anonymous FTP archive sites on the Internet store their packages in compressed tar format, so
the files will end in .tar.Z or .tar.gz. To extract the files from these files you would first uncompress
them, or use the appropriate zcat command and pipe the output into tar, e.g.:
% zcat archive.tar.Z | tar -xvf -

where the hyphen at the end of the tar command indicates that the file is taken from stdin.

Introduction to Unix  1998 University Technology Services, The Ohio State University 93
 Other Useful Commands

8.2.3 uuencode/uudecode - encode a file

To encode a binary file into 7-bit ASCII use the uuencode command. To decode the file back to
binary use the uudecode command. The uu in the names comes because they are part of the
Unix-to-Unix CoPy (UUCP) set of commands. The uuencode and uudecode commands are
commonly used when sending binary files through e-mail. In e-mail there’s no guarantee that 8-bit
binary files will be transferred cleanly. So to ensure delivery you should encode the binary file, either
directly, on the command line and then include the encoded file, or indirectly, by letting your MIME
mailer program do it for you. In a similar manner, the user decodes the file on the receiving end.

Syntax
uuencode [ source_file ] pathname_to_uudecode_to [ > new_file ]
uudecode [ -p ] encoded_file
Common Options
-p send output to standard output, rather than to the default file

Examples
The first line of encoded file includes the permission modes and name that uudecode will use when
decoding the file. The file begins and ends with the begin and end keywords, respectively, e.g.:
begin 555 binary_filename
M?T5,1@$" 0 " ( ! %"W #0 5"< T"
M!0 H !4 % 8 T $- "@ H 4 P
M -0 !$ ! ! ! %"
M%P !0A< % $ $ 4(8 -"& W& W% < 0
M @ !0B T(@ )@ !P O=7-R+VQI8B]L9"YS
M;RXQ ?< 'Y VP "O !VP )8 &6 !G0
M %[ U0 %G !3 ;< #Q %Q !
MEP :P !_ '@ !PP (P
M N0 =H _0 $D Y < #F /L
M01 $' $ & ! P #0A@ 4(8
M" ! 0 !E !@ , T(@ %"( )@ $
M 0 ( ;@ $ ' -"N !0K@ /H
M $ # ', ! P #1J 4:@ #8 !
M !Y 0 , TH %* !=X 0
M@ @ # -/X !3^ "E, $ (4 !
M 4_> )0 0 ". P
; %0 P )@ $

end

94  1998 University Technology Services, The Ohio State University Introduction to Unix
 File Archiving, Compression and Conversion

8.2.4 dd - block copy and convert

The dd command allows you to copy from raw devices, such as disks and tapes, specifying the input
and output block sizes. dd was originally known as the disk-to-disk copy program. With dd you can
also convert between different formats, for example, EBCDIC to ASCII, or swap byte order, etc.

Syntax
dd [if=input_device] [of=output_device] [operand=value]

Common Options
if=input_device the input file or device
of=output_device the output file or device

If the input or output devices are not specified they default to standard input and standard output,
respectively.

Operands can include:

ibs=n input block size (defaults to 512 byte blocks)
obs=n output block size (defaults to 512 byte blocks)
bs=n sets both input and output block sizes
files=n copy n input files
skip=n skip n input blocks before starting to copy
count=n only copy n input blocks
conv=value[,value] where value can include:
ascii convert EBCDIC to ASCII
ebcdic convert from ASCII to EBCDIC
lcase convert upper case characters to lower case
ucase convert lower case characters to upper case
swab swap every pair of bytes of input data
noerror don’t stop processing on an input error
sync pad every input block to the size of ibs, appending null bytes as needed

Block sizes are specified in bytes and may end in k, b, or w to indicate 1024 (kilo), 512 (block), or 2
(word), respectively.

Introduction to Unix  1998 University Technology Services, The Ohio State University 95
 Other Useful Commands

Examples

To copy files from one tape drive to another:

% dd if=/dev/rmt/0 of=/dev/rmt/1
20+0 records in
20+0 records out

To copy files written on a tape drive on a big endian machine, written with a block size of 20 blocks,
to a file on a little endian machine that now has the tape inserted in its drive, we would need to swap
pairs of bytes, as in:
% dd if=/dev/rmt/0 of=new_file ibs=20b conv=swab
1072+0 records in
21440+0 records out

Upon completion dd reports the number of whole blocks and partial blocks for both the input and
output files.

8.2.5 od - octal dump of a file

od dumps a file to stdout in different formats, including octal, decimal, floating point, hex, and
character format.

Syntax
od [options] file

Common Options
-b octal dump
-d|-D decimal (-d) or long decimal (-D) dump
-s|-S signed decimal (-s) and signed long decimal (-S) dump
-f|-F floating point (-f) or long (double) floating point (-F) dump
-x|-X hex (-x) or long hex (-X) dump
-c|-C character (single byte) or long character dump (single or multi-byte
characters, as determined by locale settings) dump
-v verbose mode

96  1998 University Technology Services, The Ohio State University Introduction to Unix
 File Archiving, Compression and Conversion

Examples

To look at the actual contents of the following file, a list of P. G. Wodehouse’s Lord Emsworth
novels.
Something Fresh [1915] Uncle Dynamite [1948]
Leave it to Psmith [1923] Pigs Have Wings [1952]
Summer Lightning [1929] Cocktail Time [1958]
Heavy Weather [1933] Service with a Smile [1961]
Blandings Castle and Elsewhere [1935] Galahad at Blandings [1965]
Uncle Fred in the Springtime [1939] A Pelican at Blandings [1969]
Full Moon [1947] Sunset at Blandings [1977]

we could do:
% od -c wodehouse
0000000 S o m e t h i n g F r e s h
0000020 [ 1 9 1 5 ] \t U n c l e D y n
0000040 a m i t e [ 1 9 4 8 ] \n L e a
0000060 v e i t t o P s m i t h
0000100 [ 1 9 2 3 ] \t P i g s H a v e
0000120 W i n g s [ 1 9 5 2 ] \n S u
0000140 m m e r L i g h t n i n g [
0000160 1 9 2 9 ] \t C o c k t a i l T
0000200 i m e [ 1 9 5 8 ] \n H e a v y
0000220 W e a t h e r [ 1 9 3 3 ] \t
0000240 S e r v i c e w i t h a S
0000260 m i l e [ 1 9 6 1 ] \n B l a n
0000300 d i n g s C a s t l e a n d
0000320 E l s e w h e r e [ 1 9 3 5
0000340 ] \t G a l a h a d a t B l a
0000360 n d i n g s [ 1 9 6 5 ] \n U n
0000400 c l e F r e d i n t h e
0000420 S p r i n g t i m e [ 1 9 3 9
0000440 ] \t A P e l i c a n a t B
0000460 l a n d i n g s [ 1 9 6 9 ] \n
0000500 F u l l M o o n [ 1 9 4 7 ]
0000520 \t S u n s e t a t B l a n d
0000540 i n g s [ 1 9 7 7 ] \n
0000554

Introduction to Unix  1998 University Technology Services, The Ohio State University 97
 Other Useful Commands

8.3 Remote Connections

TABLE 8.3 Remote Connection Commands

Command/Syntax What it will do

finger [options] user[@hostname] report information about users on local and remote machines
ftp [options] host transfer file(s) using file transfer protocol
rcp [options] hostname remotely copy files from this machine to another machine
rlogin [options] hostname login remotely to another machine
rsh [options] hostname remote shell to run on another machine
telnet [host [port]] communicate with another host using telnet protocol

8.3.1 TELNET and FTP - remote login and file transfer protocols
TELNET and FTP are Application Level Internet protocols. The TELNET and FTP protocol
specifications have been implemented by many different sources, including The National Center for
Supercomputer Applications (NCSA), and many other public domain and shareware sources.

The programs implementing the TELNET protocol are usually called telnet, but not always. Some
notable exceptions are tn3270, WinQVT, and QWS3270, which are also TELNET protocol
implementations. TELNET is used for remote login to other computers on the Internet.

The programs implementing the FTP protocol are usually called ftp, but there are exceptions to that
too. A program called Fetch, distributed by Dartmouth College, WS_FTP, written and distributed by
John Junod, and Ftptool, written by a Mike Sullivan, are FTP protocol implementations with graphic
user interfaces. There’s an enhanced FTP version, ncftp, that allows additional features, written by
Mike Gleason. Also, FTP protocol implementations are often included in TELNET implementation
programs, such as the ones distributed by NCSA. FTP is used for transferring files between
computers on the Internet.

rlogin is a remote login service that was at one time exclusive to Berkeley 4.3 BSD UNIX.
Essentially, it offers the same functionality as telnet, except that it passes to the remote computer
information about the user's login environment. Machines can be configured to allow connections
from trusted hosts without prompting for the users’ passwords. A more secure version of this
protocol is the Secure SHell, SSH, software written by Tatu Ylonen and available via
ftp://ftp.net.ohio-state.edu/pub/security/ssh.

From a Unix prompt, these programs are invoked by typing the command (program name) and the
(Internet) name of the remote machine to which to connect. You can also specify various options, as
allowed, for these commands.

98  1998 University Technology Services, The Ohio State University Introduction to Unix
 Remote Connections

Syntax
telnet [options] [ remote_host [ port_number ] ]
tn3270 [options] [ remote_host [ port_number ] ]
ftp [options] [ remote_host ]

Common Options
ftp telnet Action
-d set debugging mode on
-d same as above (SVR4 only)
-i turn off interactive prompting
-n don’t attempt auto-login on connection
-v verbose mode on
-l user connect with username, user, on the remote host (SVR4 only)
-8 8-bit data path (SVR4 only)

telnet and tn3270 allow you the option of specifying a port number to connect to on the remote host.
For both commands it defaults to port number 23, the telnet port. Other ports are used for debugging
of network services and for specialized resources.

Examples
telnet oscar.us.ohio-state.edu
tn3270 ohstmvsa.acs.ohio-state.edu
ftp magnus.acs.ohio-state.edu

The remote machine will query you for your login identification and your password. Machines set up
as archives for software or information distribution often allow anonymous ftp connections. You ftp
to the remote machine and login as anonymous (the login ftp is equivalent on many machines), that
is, when asked for your "login" you would type anonymous.

Once you have successfully connected to a remote computer with telnet and rlogin (and assuming
terminal emulation is appropriate) you will be able to use the machine as you always do.

Once you have successfully connected to a remote computer with ftp, you will be able to transfer a
file "up" to that computer with the put command, or "down" from that computer with the get
command. The syntax is as follows:
put local-file-name remote-file-name
get local-file-name remote-file-name

Introduction to Unix  1998 University Technology Services, The Ohio State University 99
 Other Useful Commands

Other commands are available in ftp as well, depending on the specific "local" and "remote" FTP
implementations. The help command will display a list of available commands. The help command
will also display the purpose of a specific command. Examples of valid commands are shown below:
help display list of available commands
help mget display the purpose of the mget command ("get multiple files")
pwd present working directory
ls or dir directory list
cd change directory
lcd local change directory
open specify the machine you wish to connect with
user specify your login id (in cases where you are not prompted)
quit quit out of the FTP program

8.3.2 finger - get information about users

finger displays the .plan file of a specific user, or reports who is logged into a specific machine. The
user must allow general read permission on the .plan file.

Syntax
finger [options] [user[@hostname]]

Common Options
-l force long output format
-m match username only, not first or last names
-s force short output format

Examples
brigadier: condron [77]> finger workshop@nyssa
This is a sample .plan file for the nyssa id, workshop.
This id is being used this week by Frank Fiamingo, Linda
DeBula, and Linda Condron, while we teach a pilot version
of the new Unix workshop we developed for UTS.

Hope yer learnin' somethin'.

Frank, Linda, & Linda

brigadier: condron [77]> finger

Login Name TTY Idle When Where
condron Linda S Condron p0 Sun 18:13 lcondron-mac.acs
frank Frank G. Fiamingo p1 Mon 16:19 nyssa

100  1998 University Technology Services, The Ohio State University Introduction to Unix
 Remote Connections

8.3.3 Remote commands

A number of Unix machines can be connected together to form a local area network. When this is the
case, it often happens that a user of one machine has valid login access to several of the other
machines in the local network. There are Unix commands available to such users which provide
convenience in carrying out certain common operations. Because these commands focus on
communications with remote hosts in the local network, the command names begin with the letter
"r": rlogin, rsh, and rcp. The remote access capability of these commands is supported (optionally)
by the dotfile, ~/.rhosts, for individual users and by the system-wide file /etc/hosts.equiv. For
security reasons these may be restricted on some hosts.

The rlogin command allows remote login access to another host in the local network. rlogin passes
information about the local environment, including the value of the TERM environment variable, to
the remote host.

The rsh command provides the ability to invoke a Unix shell on a remote host in the local network for
the purpose of executing a shell command there. This capability is similar to the "shell escape"
function commonly available from within such Unix software systems as editors and email.

The rcp command provides the ability to copy files from the local host to a remote host in the local
network.

Syntax
rlogin [ -l username ] remote_host
rsh [ -l username ] remote_host [ command ]
rcp [ [user1]@host1:]original_filename [ [user2]@host2:]new_filename

where the parts in brackets ([]) are optional. rcp does not prompt for passwords, so you must have
permission to execute remote commands on the specified machines as the selected user on each
machine.

Common Options
-l username connect as the user, username, on the remote host (rlogin & rsh)

The .rhosts file, if it exists in the user's home directory on the remote host, permits rlogin, rsh, or rcp
access to that remote host without prompting for a password for that account. The .rhosts file
contains an entry for each remote host and username from which the owner of the .rhosts file may
wish to connect. Each entry in the .rhosts file is of the form:
remote_host remote_user

where listing the remote_user is optional. For instance, if Heather Jones wants to be able to connect
to machine1 (where her username is heather) from machine2 (where her username is jones), or from
machine 3 (where her username is heather, the same as for machine1), she could create a .rhosts file
in her home directory on machine1. The contents of this file could be:

Introduction to Unix  1998 University Technology Services, The Ohio State University 101
 Other Useful Commands

machine2 jones
machine3

--or--
machine2 jones
machine3 heather

On a system-wide basis the file /etc/hosts.equiv serves the same purpose for all users, except the
super-user. Such a file with the contents:
remote_machine

allows any user from remote_machine to remote connect to this machine without a password, as the
same username on this machine.

An /etc/hosts.equiv file with the contents:

remote_machine remote_user

allows remote_user, on remote_machine, to remote connect to this machine as any local user, except
the super-user.

/etc/hosts.equiv and ~/.rhosts files should be used with caution.

The Secure SHell (SSH) versions of the rcp, rsh, and rlogin programs are freely available and
provide much greater security.

102  1998 University Technology Services, The Ohio State University Introduction to Unix
 Shell Scripts

CHAPTER 9 Shell Programming

9.1 Shell Scripts

You can write shell programs by creating scripts containing a series of shell commands. The first line
of the script should start with #! which indicates to the kernel that the script is directly executable.
You immediately follow this with the name of the shell, or program (spaces are allowed), to execute,
using the full path name. Generally you can count on having up to 32 characters, possibly more on
some systems, and can include one option. So to set up a Bourne shell script the first line would be:
#! /bin/sh

or for the C shell:

#! /bin/csh -f

where the "-f" option indicates that it should not read your .cshrc. Any blanks following the magic
symbols, #!, are optional.

You also need to specify that the script is executable by setting the proper bits on the file with chmod,
e.g.:
% chmod +x shell_script

Within the scripts # indicates a comment from that point until the end of the line, with #! being a
special case if found as the first characters of the file.

9.2 Setting Parameter Values

Parameter values, e.g. param, are assigned as:

Bourne shell C shell
param=value set param = value

where value is any valid string, and can be enclosed within quotations, either single (’value) or
double ("value"), to allow spaces within the string value. When enclosed with backquotes (‘value‘)
the string is first evaluated by the shell and the result is substituted. This is often used to run a
command, substituting the command output for value, e.g.:

Introduction to Unix  1998 University Technology Services, The Ohio State University 103
 Shell Programming

$ day=‘date +%a‘
$ echo $day
Wed

After the parameter values has been assigned the current value of the parameter is accessed using the
$param, or ${param}, notation.

9.3 Quoting
We quote strings to control the way the shell interprets any parameters or variables within the string.
We can use single (’) and double (") quotes around strings. Double quotes define the string, but
allow variable substitution. Single quotes define the string and prevent variable substitution. A
backslash (\) before a character is said to escape it, meaning that the system should take the character
literally, without assigning any special meaning to it. These quoting techniques can be used to
separate a variable from a fixed string. As an example lets use the variable, var, that has been
assigned the value bat, and the constant string, man. If I wanted to combine these to get the result
"batman" I might try:
$varman

but this doesn’t work, because the shell will be trying to evaluate a variable called varman, which
doesn’t exist. To get the desired result we need to separate it by quoting, or by isolating the variable
with curly braces ({}), as in:
"$var"man - quote the variable
$var""man - separate the parameters
$var"man" - quote the constant
$var''man - separate the parameters
$var'man' - quote the constant
$var\man - separate the parameters
${var}man - isolate the variable

These all work because ", ’, \, {, and } are not valid characters in a variable name.

We could not use either of

’$var’man
\$varman

because it would prevent the variable substitution from taking place.

When using the curly braces they should surround the variable only, and not include the $, otherwise,
they will be included as part of the resulting string, e.g.:
% echo {$var}man
{bat}man

104  1998 University Technology Services, The Ohio State University Introduction to Unix
 Variables

9.4 Variables
There are a number of variables automatically set by the shell when it starts. These allow you to
reference arguments on the command line.

These shell variables are:

TABLE 9.1 Shell Variables

Variable Usage sh csh

$# number of arguments on the command line x
$- options supplied to the shell x
$? exit value of the last command executed x
$$ process number of the current process x x
$! process number of the last command done in background x
$n argument on the command line, where n is from 1 through 9, reading left to right x x
$0 the name of the current shell or program x x
$* all arguments on the command line ("$1 $2 ... $9") x x
$@ all arguments on the command line, each separately quoted ("$1" "$2" ... "$9") x
$argv[n] selects the nth word from the input list x
${argv[n]} same as above x
$#argv report the number of words in the input list x

We can illustrate these with some simple scripts. First for the Bourne shell the script will be:
#!/bin/sh
echo "$#:" $#
echo '$#:' $#
echo '$-:' $-
echo '$?:' $?
echo '$$:' $$
echo '$!:' $!
echo '$3:' $3
echo '$0:' $0
echo '$*:' $*
echo '$@:' $@

Introduction to Unix  1998 University Technology Services, The Ohio State University 105
 Shell Programming

When executed with some arguments it displays the values for the shell variables, e.g.:
$ ./variables.sh one two three four five
5: 5
$#: 5
$-:
$?: 0
$$: 12417
$!:
$3: three
$0: ./variables.sh
$*: one two three four five
$@: one two three four five

As you can see, we needed to use single quotes to prevent the shell from assigning special meaning to
$. The double quotes, as in the first echo statement, allowed substitution to take place.

Similarly, for the C shell variables we illustrate variable substitution with the script:
#!/bin/csh -f
echo '$$:' $$
echo '$3:' $3
echo '$0:' $0
echo '$*:' $*
echo '$argv[2]:' $argv[2]
echo '${argv[4]}:' ${argv[4]}
echo '$#argv:' $#argv

which when executed with some arguments displays the following:

% ./variables.csh one two three four five
$$: 12419
$3: three
$0: ./variables.csh
$*: one two three four five
$argv[2]: two
${argv[4]}: four
$#argv: 5

106  1998 University Technology Services, The Ohio State University Introduction to Unix
 Parameter Substitution

9.5 Parameter Substitution

You can reference parameters abstractly and substitute values for them based on conditional settings
using the operators defined below. Again we will use the curly braces ({}) to isolate the variable and
its operators.

$parameter substitute the value of parameter for this string

${parameter} same as above. The brackets are helpful if there’s no separation
between this parameter and a neighboring string.
$parameter= sets parameter to null.
${parameter-default} if parameter is not set, then use default as the value here. The
parameter is not reset.
${parameter=default} if parameter is not set, then set it to default and use the new value
${parameter+newval) if parameter is set, then use newval, otherwise use nothing here.
The parameter is not reset.
${parameter?message} if parameter is not set, then display message. If parameter is set,
then use its current value.

There are no spaces in the above operators. If a colon (:) is inserted before the -, =, +, or ? then a test
if first performed to see if the parameter has a non-null setting.

The C shell has a few additional ways of substituting parameters:

$list[n] selects the nth word from list
${list[n]} same as above
$#list report the number of words in list
$?parameter return 1 if parameter is set, 0 otherwise
${?parameter} same as above
$< read a line from stdin

The C shell also defines the array, $argv[n] to contain the n arguments on the command line and
$#argv to be the number of arguments, as noted in Table 9.1.

Introduction to Unix  1998 University Technology Services, The Ohio State University 107
 Shell Programming

To illustrate some of these features we’ll use the test script below.
#!/bin/sh
param0=$0
test -n "$1" && param1=$1
test -n "$2" && param2=$2
test -n "$3" && param3=$3
echo 0: $param0
echo "1: ${param1-1}: \c" ;echo $param1
echo "2: ${param2=2}: \c" ;echo $param2
echo "3: ${param3+3}: \c" ;echo $param3

In the script we first test to see if the variable exists, if so we set a parameter to its value. Below this
we report the values, allowing substitution.

In the first run through the script we won’t provide any arguments:
$ ./parameter.sh
0: ./parameter.sh # always finds $0
1: 1: # substitute 1, but don’t assign this value
2: 2: 2 # substitute 2 and assign this value
3: : # don’t substitute

In the second run through the script we’ll provide the arguments:
$ ./parameter one two three
0: ./parameter.sh # always finds $0
1: one: one # don’t substitute, it already has a value
2: two: two # don’t substitute, it already has a value
3: 3: three # substitute 3, but don’t assign this value

108  1998 University Technology Services, The Ohio State University Introduction to Unix
 Here Document

9.6 Here Document

A here document is a form of quoting that allows shell variables to be substituted. It’s a special form
of redirection that starts with <<WORD and ends with WORD as the only contents of a line. In the
Bourne shell you can prevent shell substitution by escaping WORD by putting a \ in front of it on the
redirection line, i.e. <<\WORD, but not on the ending line. To have the same effect the C shell
expects the \ in front of WORD at both locations.

The following scripts illustrate this,

for the Bourne shell: and for the C shell:

#!/bin/sh #!/bin/csh -f
does=does set does = does
not="" set not = ""
cat << EOF cat << EOF
This here document This here document
$does $not $does $not
do variable substitution do variable substitution
EOF EOF
cat << \EOF cat << \EOF
This here document This here document
$does $not $does $not
do variable substitution do variable substitution
EOF \EOF

Both produce the output:

This here document
does
do variable substitution
This here document
$does $not
do variable substitution

In the top part of the example the shell variables $does and $not are substituted. In the bottom part
they are treated as simple text strings without substitution.

Introduction to Unix  1998 University Technology Services, The Ohio State University 109
 Shell Programming

9.7 Interactive Input

Shell scripts will accept interactive input to set parameters within the script.

9.7.1 Sh
Sh uses the built-in command, read, to read in a line, e.g.:
read param

We can illustrate this with the simple script:

#!/bin/sh
echo "Input a phrase \c" # This is /bin/echo which requires "\c" to prevent <newline>
read param
echo param=$param

When we run this script it prompts for input and then echoes the results:
$ ./read.sh
Input a phrase hello frank # I type in hello frank <return>
param=hello frank

9.7.2 Csh
Csh uses the $< symbol to read a line from stdin, e.g.:
set param = $<

The spaces around the equal sign are important. The following script illustrates how to use this.
#!/bin/csh -f
echo -n "Input a phrase " # This built-in echo requires -n to prevent <newline>
set param = $<
echo param=$param

Again, it prompts for input and echoes the results:

% ./read.csh
Input a phrase hello frank # I type in hello frank <return>
param=hello frank

110  1998 University Technology Services, The Ohio State University Introduction to Unix
 Functions

9.8 Functions
The Bourne shell has functions. These are somewhat similar to aliases in the C shell, but allow you
more flexibility. A function has the form:
fcn () { command; }

where the space after {, and the semicolon (;) are both required; the latter can be dispensed with if a
<newline> precedes the }. Additional spaces and <newline>’s are allowed. We saw a few examples
of this in the sample .profile in an earlier chapter, where we had functions for ls and ll:
ls() { /bin/ls -sbF "$@";}
ll() { ls -al "$@";}

The first one redefines ls so that the options -sbF are always supplied to the standard /bin/ls
command, and acts on the supplied input, "$@". The second one takes the current value for ls (the
previous function) and tacks on the -al options.

Functions are very useful in shell scripts. The following is a simplified version of one I use to
automatically backup up system partitions to tape.
#!/bin/sh
# Cron script to do a complete backup of the system
HOST=`/bin/uname -n`
admin=frank
Mt=/bin/mt
Dump=/usr/sbin/ufsdump
Mail=/bin/mailx
device=/dev/rmt/0n
Rewind="$Mt -f $device rewind"
Offline="$Mt -f $device rewoffl"
# Failure - exit
failure () {
$Mail -s "Backup Failure - $HOST" $admin << EOF_failure
$HOST
Cron backup script failed. Apparently there was no tape in the device.

EOF_failure
exit 1
}

# Dump failure - exit

dumpfail () {

Introduction to Unix  1998 University Technology Services, The Ohio State University 111
 Shell Programming

$Mail -s "Backup Failure - $HOST" $admin << EOF_dumpfail

$HOST
Cron backup script failed. Initial tape access was okay, but dump failed.
EOF_dumpfail
exit 1
}
# Success
success () {
$Mail -s "Backup completed successfully - $HOST" $admin << EOF_success
$HOST
Cron backup script was apparently successful. The /etc/dumpdates file is:
`/bin/cat /etc/dumpdates`
EOF_success
}
# Confirm that the tape is in the device
$Rewind || failure
$Dump 0uf $device / || dumpfail
$Dump 0uf $device /usr || dumpfail
$Dump 0uf $device /home || dumpfail
$Dump 0uf $device /var || dumpfail
($Dump 0uf $device /var/spool/mail || dumpfail) && success
$Offline

This script illustrates a number of topics that we’ve looked at in this document. It starts by setting
various parameter values. HOST is set from the output of a command, admin is the administrator of
the system, Mt, Dump, and Mail are program names, device is the special device file used to access
the tape drive, Rewind and Offline contain the commands to rewind and off-load the tape drive,
respectively, using the previously referenced Mt and the necessary options. There are three functions
defined: failure, dumpfail, and success. The functions in this script all use a here document to form
the contents of the function. We also introduce the logical OR (||) and AND (&&) operators here;
each is position between a pair of commands. For the OR operator, the second command will be run
only if the first command does not complete successfully. For the AND operator, the second
command will be run only if the first command does complete successfully.

The main purpose of the script is done with the Dump commands, i.e. backup the specified file
systems. First an attempt is made to rewind the tape. Should this fail, || failure, the failure function
is run and we exit the program. If it succeeds we proceed with the backup of each partition in turn,
each time checking for successful completion (|| dumpfail). Should it not complete successfully we
run the dumpfail subroutine and then exit. If the last backup succeeds we proceed with the success
function ((...) && success). Lastly, we rewind the tape and take it offline so that no other user can
accidently write over our backup tape.

112  1998 University Technology Services, The Ohio State University Introduction to Unix
 Control Commands

9.9 Control Commands

9.9.1 Conditional if
The conditional if statement is available in both shells, but has a different syntax in each.

9.9.1.1 Sh
if condition1
then
command list if condition1 is true
[elif condition2
then command list if condition2 is true]
[else
command list if condition1 is false]
fi
The conditions to be tested for are usually done with the test, or [] command (see Section 8.9.6). The
if and then must be separated, either with a <newline> or a semicolon (;).
#!/bin/sh
if [ $# -ge 2 ]
then
echo $2
elif [ $# -eq 1 ]; then
echo $1
else
echo No input
fi

There are required spaces in the format of the conditional test, one after [ and one before ]. This script
should respond differently depending upon whether there are zero, one or more arguments on the
command line. First with no arguments:
$ ./if.sh
No input

Now with one argument:

$ ./if.sh one
one

And now with two arguments:

$ ./if.sh one two
two

Introduction to Unix  1998 University Technology Services, The Ohio State University 113
 Shell Programming

9.9.1.2 Csh
if (condition) command
-or-
if (condition1) then
command list if condition1 is true
[else if (condition2) then
command list if condition2 is true]
[else
command list if condition1 is false]
endif

The if and then must be on the same line.

#!/bin/csh -f
if ( $#argv >= 2 ) then
echo $2
else if ( $#argv == 1 ) then
echo $1
else
echo No input
endif

Again, this script should respond differently depending upon whether I have zero, one or more
arguments on the command line. First with no arguments:
% ./if.csh
No input

Now with one argument:

% ./if.csh one
one

And now with two arguments:

% ./if.csh one two
two

114  1998 University Technology Services, The Ohio State University Introduction to Unix
 Control Commands

9.9.2 Conditional switch and case

To choose between a set of string values for a parameter use case in the Bourne shell and switch in
the C shell.

9.9.2.1 Sh
case parameter in
pattern1[|pattern1a]) command list1;;
pattern2) command list2
command list2a;;
pattern3) command list3;;
*) ;;
esac

You can use any valid filename meta-characters within the patterns to be matched. The ;; ends each
choice and can be on the same line, or following a <newline>, as the last command for the choice.
Additional alternative patterns to be selected for a particular case are separated by the vertical bar, |,
as in the first pattern line in the example above. The wildcard symbols,: ? to indicate any one
character and * to match any number of characters, can be used either alone or adjacent to fixed
strings.

This simple example illustrates how to use the conditional case statement.
#!/bin/sh
case $1 in
aa|ab) echo A
;;
b?) echo "B \c"
echo $1;;
c*) echo C;;
*) echo D;;
esac

So when running the script with the arguments on the left, it will respond as on the right:
aa A
ab A
ac D
bb B bb
bbb D
c C
cc C
fff D

Introduction to Unix  1998 University Technology Services, The Ohio State University 115
 Shell Programming

9.9.2.2 Csh
switch (parameter)
case pattern1:
command list1
[breaksw]
case pattern2:
command list2
[breaksw]
default:
command list for default behavior
[breaksw]
endsw

breaksw is optional and can be used to break out of the switch after a match to the string value of the
parameter is made. Switch doesn’t accept "|" in the pattern list, but it will allow you to string several
case statements together to provide a similar result. The following C shell script has the same
behavior as the Bourne shell case example above.
#!/bin/csh -f
switch ($1)
case aa:
case ab:
echo A
breaksw
case b?:
echo -n "B "
echo $1
breaksw
case c*:
echo C
breaksw
default:
echo D
endsw

116  1998 University Technology Services, The Ohio State University Introduction to Unix
 Control Commands

9.9.3 for and foreach

One way to loop through a list of string values is with the for and foreach commands.

9.9.3.1 Sh
for variable [in list_of_values]
do
command list
done

The list_of_values is optional, with $@ assumed if nothing is specified. Each value in this list is
sequentially substituted for variable until the list is emptied. Wildcards can be used and are applied
to file names in the current directory. Below we illustrate the for loop in copying all files ending in
.old to similar names ending in .new. In these examples the basename utility extracts the base part of
the name so that we can exchange the endings.
#!/bin/sh
for file in *.old
do
newf=`basename $file .old`
cp $file $newf.new
done

9.9.3.2 Csh
foreach variable (list_of_values)
command list
end

The equivalent C shell script to copy all files ending in .old to .new is:
#!/bin/csh -f
foreach file (*.old)
set newf = `basename $file .old`
cp $file $newf.new
end

Introduction to Unix  1998 University Technology Services, The Ohio State University 117
 Shell Programming

9.9.4 while
The while commands let you loop as long as the condition is true.

9.9.4.1 Sh
while condition
do
command list
[break]
[continue]
done

A simple script to illustrate a while loop is:

#!/bin/sh
while [ $# -gt 0 ]
do
echo $1
shift
done

This script takes the list of arguments, echoes the first one, then shifts the list to the left, losing the
original first entry. It loops through until it has shifted all the arguments off the argument list.
$ ./while.sh one two three
one
two
three

118  1998 University Technology Services, The Ohio State University Introduction to Unix
 Control Commands

9.9.4.2 Csh
while (condition)
command list
[break]
[continue]
end

If you want the condition to always be true specify 1 within the conditional test.

A C shell script equivalent to the one above is:

#!/bin/csh -f
while ($#argv != 0 )
echo $argv[1]
shift
end

9.9.5 until
This looping feature is only allowed in the Bourne shell.
until condition
do
command list while condition is false
done

The condition is tested at the start of each loop and the loop is terminated when the condition is true.
A script equivalent to the while examples above is:
#!/bin/sh
until [ $# -le 0 ]
do
echo $1
shift
done

Notice, though, that here we’re testing for less than or equal, rather than greater than or equal,
because the until loop is looking for a false condition.

Both the until and while loops are only executed if the condition is satisfied. The condition is
evaluated before the commands are executed.

Introduction to Unix  1998 University Technology Services, The Ohio State University 119
 Shell Programming

9.9.6 test
Conditional statements are evaluated for true or false values. This is done with the test, or its
equivalent, the [] operators. It the condition evaluates to true, a zero (TRUE) exit status is set,
otherwise a non-zero (FALSE) exit status is set. If there are no arguments a non-zero exit status is
set. The operators used by the Bourne shell conditional statements are given below.

For filenames the options to test are given with the syntax:
-option filename

The options available for the test operator for files include:
-r true if it exists and is readable
-w true if it exists and is writable
-x true if it exists and is executable
-f true if it exists and is a regular file (or for csh, exists and is not a directory)
-d true if it exists and is a directory
-h or -L true if it exists and is a symbolic link
-c true if it exists and is a character special file (i.e. the special device is accessed
one character at a time)
-b true if it exists and is a block special file (i.e. the device is accessed in blocks
of data)
-p true if it exists and is a named pipe (fifo)
-u true if it exists and is setuid (i.e. has the set-user-id bit set, s or S in the third
bit)
-g true if it exists and is setgid (i.e. has the set-group-id bit set, s or S in the sixth
bit)
-k true if it exists and the sticky bit is set (a t in bit 9)
-s true if it exists and is greater than zero in size

There is a test for file descriptors:

-t [file_descriptor] true if the open file descriptor (default is 1, stdin) is associated with a terminal

There are tests for strings:

-z string true if the string length is zero
-n string true if the string length is non-zero
string1 = string2 true if string1 is identical to string2
string1 != string2 true if string1 is non identical to string2
string true if string is not NULL

120  1998 University Technology Services, The Ohio State University Introduction to Unix
 Control Commands

There are integer comparisons:

n1 -eq n2 true if integers n1 and n2 are equal
n1 -ne n2 true if integers n1 and n2 are not equal
n1 -gt n2 true if integer n1 is greater than integer n2
n1 -ge n2 true if integer n1 is greater than or equal to integer n2
n1 -lt n2 true if integer n1 is less than integer n2
n1 -le n2 true if integer n1 is less than or equal to integer n2

The following logical operators are also available:

! negation (unary)
-a and (binary)
-o or (binary)
() expressions within the () are grouped together. You may need to quote the ()
to prevent the shell from interpreting them.

Introduction to Unix  1998 University Technology Services, The Ohio State University 121
 Shell Programming

9.9.7 C Shell Logical and Relational Operators

The C shell has its own set of built-in logical and relational expression operators. In descending order
of precedence they are:
(...) group expressions with ()
~ inversion (one’s complement)
! logical negation
*, /, % multiply, divide, modulus
+, - add, subtract
<<, >> bitwise shift left, bitwise shift right
<= less than or equal
>= greater than or equal
< less than
> greater than
== equal
!= not equal
=~ match a string
!~ don’t match the string
& bitwise AND
^ bitwise XOR (exclusive or)
| bitwise OR
&& logical AND
|| logical OR
{command} true (1) if command terminates with a zero exit status, false (0) otherwise.

The C shell also allows file type and permission inquiries with the operators:
-r return true (1) if it exists and is readable, otherwise return false (0)
-w true if it exists and is writable
-x true if it exists and is executable
-f true if it exists and is a regular file (or for csh, exists and is not a directory)
-d true if it exists and is a directory
-e true if the file exists
-o true if the user owns the file
-z true if the file has zero length (empty)

122  1998 University Technology Services, The Ohio State University Introduction to Unix
C H A P T E R 10 Editors

There are numerous text processing utilities available with Unix, as is noted throughout this
document (e.g., ed, ex, sed, awk, the grep family, and the roff family). Among the editors, the
standard "visual" (or fullscreen) editor on Unix is vi. It comprises a super-set, so to speak, of ed and
ex (the Unix line editors) capabilities.

Vi is a modal editor. This means that it has specific modes that allow text insertion, text deletion, and
command entering. You leave the insert mode by typing the <escape> key. This brings you back to
command mode. The line editor, ex, is incorporated within vi. You can switch back and forth
between full-screen and line mode as desired. In vi mode type Q to go to ex mode. In ex mode at the
: prompt type vi to return to vi mode. There is also a read-only mode of vi, which you can invoke as
view.

Another editor that is common on Unix systems, especially in college and university environments, is
emacs (which stands for "editing macros"). While vi usually comes with the Unix operating system,
emacs usually does not. It is distributed by The Free Software Foundation. It is arguably the most
powerful editor available for Unix. It is also a very large software system, and is a heavy user of
computer system resources.

The Free Software Foundation and the GNU Project (of which emacs is a part) were founded by
Richard Stallman and his associates, who believe (as stated in the GNU Manifesto) that sharing
software is the "fundamental act of friendship among programmers." Their General Public License
guarantees your rights to use, modify, and distribute emacs (including its source code), and was
specifically designed to prevent anyone from hoarding or turning a financial profit from emacs or any
software obtained through the Free Software Foundation. Most of their software, including emacs, is
available at ftp://ftp.gnu.org/pub/gnu/ and http://www.gnu.org/.

Both vi and emacs allow you to create start-up files that you can populate with macros to control
settings and functions in the editors.

Introduction to Unix  1998 University Technology Services, The Ohio State University 123
 Editors

10.1 Configuring Your vi Session

To configure the vi environment certain options can be set with the line editor command :set during a
vi editing session. Alternatively, frequently used options can be set automatically when vi is invoked,
by use of the .exrc file. This file can also contain macros to map keystrokes into functions using the
map function. Within vi these macros can be defined with the :map command. Control characters
can be inserted by first typing <control>-V (^V), then the desired control character. The options
available in vi include, but are not limited to, the following. Some options are not available on every
Unix system.
:set all display all option settings
:set ignorecase ignore the case of a character in a search
:set list display tabs and carriage returns
:set nolist turn off list option
:set number display line numbers
:set nonumber turn off line numbers
:set showmode display indication that insert mode is on
:set noshowmode turn off showmode option
:set wrapmargin=n turn on word-wrap n spaces from the right margin
:set wrapmargin=0 turn off wrapmargin option
:set warn display "No write since last change"
:set nowarn turn off "write" warning

The following is a sample .exrc file:

set wrapmargin=10
set number
set list
set warn
set ignorecase
map K {!}fmt -80 # reformat this paragraph, {!}, using fmt to 80 characters per line
map ^Z :!spell # invoke spell, :!, to check a word spelling (return to vi with ^D)

124  1998 University Technology Services, The Ohio State University Introduction to Unix
 Configuring Your emacs Session

10.2 Configuring Your emacs Session

Configuring the emacs environment amounts to making calls to LISP functions. Emacs is infinitely
customizable by means of emacs variables and built-in functions and by using Emacs LISP
programming. Settings can be specified from the minibuffer (or command line) during an emacs
session. Alternatively, frequently used settings can be established automatically when emacs is
invoked, by use of a .emacs file. Though a discussion of Emacs LISP is beyond the scope of this
document, a few examples of common emacs configurations follow.

To set or toggle emacs variables, or to use emacs built-in functions, use the <escape> key ("Meta" is
how emacs refers to it), followed by the letter x, then by the variable or function and its arguments.
M-x what-line what line is the cursor on?
M-x auto-fill-mode turn on word-wrap
M-x auto-fill-mode turn off word-wrap
M-x set-variable<return>
fill-column<return> set line-length to
45 45 characters
M-x set-variable<return>
auto-save-interval<return> save the file automatically after every
300 300 keystrokes
M-x goto-line<return>16 move the cursor to line 16
M-x help-for-help invoke emacs help when C-h has been bound to the
backspace key

The following is a sample .emacs file:

(message "Loading ~/.emacs...")
; Comments begin with semi-colons and continue to the end of the line.
(setq text-mode-hook 'turn-on-auto-fill) ;turn on word-wrap
(setq fill-column 45) ;line-length=45 chars
(setq auto-save-interval 300) ;save after every 300 keystrokes
; Bind (or map) the rubout (control-h) function to the backspace key
(global-set-key "\C-h" 'backward-delete-char-untabify)
; Bind the emacs help function to the keystroke sequence "C-x ?".
(global-set-key "\C-x?" 'help-for-help)
; To jump to line 16, type M-#<return>16
(global-set-key "\M-#" 'goto-line)
; To find out what line you are on, type M-n
(global-set-key "\M-n" 'what-line)
(message "~/.emacs loaded.")
(message "")

Introduction to Unix  1998 University Technology Services, The Ohio State University 125
 10.3 vi Quick Reference Guide
Introduction to Unix

Inserting Text: ~ changes the case of the current character

All commands in vi are preceded by pressing the i insert text before the cursor J joins the current line and the next line
escape key. Each time a different command is to
a append text after the cursor (does not u undo the last command just done on this
be entered, the escape key needs to be used. overwrite other text) line
Except where indicated, vi is case sensitive.
I insert text at the beginning of the line . repeats last change
A append text to the end of the line s substitutes text for current character
Cursor Movement Commands:
r replace the character under the cursor S substitutes text for current line
(n) indicates a number, and is optional with the next character typed
:s substitutes new word(s) for old
(n)h left (n) space(s) R Overwrite characters until the end of the :<line nos effected> s/old/new/g
line (or until escape is pressed to change
 1998 University Technology Services, The Ohio State University

(n)j down (n) space(s) command) & repeats last substitution (:s) command.
(n)k up (n) space(s) o (alpha o) open new line after the current (n)yy yanks (n) lines to buffer
line to type text
(n)l right (n) space(s) y(n)w yanks (n) words to buffer
O (alpha O) open new line before the cur-

vi Quick Reference Guide

(The arrow keys usually work also) rent line to type text p puts yanked or deleted text after cursor
^F forward one screen Deleting Text: P puts yanked or deleted text before cursor
^B back one screen dd deletes current line File Manipulation:
^D down half screen (n)dd deletes (n) line(s) :w (file) writes changes to file (default is
current file)
^U up half screen (n)dw deletes (n) word(s)
:wq writes changes to current file
(^ indicates control key; case does not matter) D deletes from cursor to end of line and quits edit session
H beginning of top line of screen x deletes current character :w! (file) overwrites file (default is cur-
rent file)
M beginning of middle line of screen (n)x deletes (n) character(s)
:q quits edit session w/no changes
L beginning of last line of screen X deletes previous character made
G beginning of last line of file Change Commands: :q! quits edit session and discards
changes
(n)G move to beginning of line (n) (n)cc changes (n) characters on line(s) until
end of the line (or until escape is pressed) :n edits next file in argument list
0 (zero) beginning of line
cw changes characters of word until end of :f (name) changes name of current file to
$ end of line the word (or until escape is pressed) (name)
(n)w forward (n) word(s) (n)cw changes characters of the next :r (file) reads contents of file into cur-
(n) words rent edit at the current cursor
(n)b back (n) word(s) position (insert a file)
c$ changes text to the end of the line
e end of word :!(command) shell escape
ct(x) changes text to the letter (x)
:r!(command) inserts result of shell command
C changes remaining text on the current at cursor position
line (until stopped by escape key)
126

ZZ write changes to current file and exit

 127 10.4 emacs Quick Reference Guide
Other Important Functions
Emacs commands are accompanied either by simultaneously holding down M-(n) repeat the next command (n) times
the control key (indicated by C-) or by first hitting the escape key C-d delete a character
(indicated by M-).
M-d delete a word
 1998 University Technology Services, The Ohio State University

C-k kill line

Essential Commands
M-k kill sentence
C-h help
C-s search forward
C-x u undo
C-r search in reverse
C-x C-g get out of current operation or command
M-% query replace
C-x C-s save the file
M-c capitalize word
C-x C-c close Emacs
M-u uppercase word

emacs Quick Reference Guide

M-l lowercase word
Cursor movement
C-t transpose characters
C-f forward one character
M-t transpose words
C-b back one character
C-@ mark beginning of region
C-p previous line
C-w cut--wipe out everything from mark to point
C-n next line
C-y paste--yank deleted text into current location
C-a beginning of line
M-q reformat paragraph
C-e end of line
M-g reformat each paragraph in region
C-l center current line on screen
M-x auto-fill-mode turn on word wrap
C-v scroll forward
M-x set-variable <return> fill-column <return> 45
M-v scroll backward
set length of lines to 45 characters
M-f forward one word
M-b back one word M-x goto-line <return> 16 move cursor to line 16
M-w copy region marked
M-a beginning of sentence
Introduction to Unix

C-x C-f find file and read it

M-e end of sentence
C-x C-v find and read alternate file
M-{ beginning of paragraph
C-x i insert file at cursor position
M-} end of paragraph
C-x C-s save file
M-< beginning of buffer
C-x C-w write buffer to a different file
M-> end of buffer
C-x C-c exit emacs, and be prompted to save
 Unix Command Summary

CHA P TE R 1 1 Unix Command Summary

11.1 Unix Commands

In the table below we summarize the more frequently used commands on a Unix system. In this
table, as in general, for most Unix commands, file, could be an actual file name, or a list of file names,
or input/output could be redirected to or from the command.

TABLE 11.1 Unix Commands

Command/Syntax What it will do

awk/nawk [options] file scan for patterns in a file and process the results
cat [options] file concatenate (list) a file
cd [directory] change directory
chgrp [options] group file change the group of the file
chmod [options] file change file or directory access permissions
chown [options] owner file change the ownership of a file; can only be done by the superuser
chsh (passwd -e/-s) username login_shell change the user’s login shell (often only by the superuser)
cmp [options] file1 file2 compare two files and list where differences occur (text or binary files)
compress [options] file compress file and save it as file.Z
cp [options] file1 file2 copy file1 into file2; file2 shouldn't already exist. This command creates
or overwrites file2.
cut (options) [file(s)] cut specified field(s)/character(s) from lines in file(s)
date [options] report the current date and time
dd [if=infile] [of=outfile] [oper- copy a file, converting between ASCII and EBCDIC or swapping byte
and=value] order, as specified
diff [options] file1 file2 compare the two files and display the differences (text files only)
df [options] [resource] report the summary of disk blocks and inodes free and in use
du [options] [directory or file] report amount of disk space in use
echo [text string] echo the text string to stdout
ed or ex [options] file Unix line editors
emacs [options] file full-screen editor
expr arguments evaluate the arguments. Used to do arithmetic, etc. in the shell.
file [options] file classify the file type

128  1998 University Technology Services, The Ohio State University Introduction to Unix
 Unix Commands

TABLE 11.1 Unix Commands

Command/Syntax What it will do

find directory [options] [actions] find files matching a type or pattern
finger [options] user[@hostname] report information about users on local and remote machines
ftp [options] host transfer file(s) using file transfer protocol
grep [options] 'search string' argument search the argument (in this case probably a file) for all occurrences of
egrep [options] 'search string' argument the search string, and list them.

fgrep [options] 'search string' argument

gzip [options] file compress or uncompress a file. Compressed files are stored with a .gz
gunzip [options] file ending

zcat [options] file

head [-number] file display the first 10 (or number of) lines of a file
hostname display or set (super-user only) the name of the current machine
kill [options] [-SIGNAL] [pid#] [%job] send a signal to the process with the process id number (pid#) or job con-
trol number (%n). The default signal is to kill the process.
ln [options] source_file target link the source_file to the target
lpq [options] show the status of print jobs
lpstat [options]
lpr [options] file print to defined printer
lp [options] file
lprm [options] remove a print job from the print queue
cancel [options]
ls [options] [directory or file] list directory contents or file permissions
mail [options] [user] simple email utility available on Unix systems. Type a period as the first
mailx [options] [user] character on a new line to send message out, question mark for help.

Mail [options] [user]

man [options] command show the manual (man) page for a command
mkdir [options] directory make a directory
more [options] file page through a text file
less [options] file
pg [options] file
mv [options] file1 file2 move file1 into file2
od [options] file octal dump a binary file, in octal, ASCII, hex, decimal, or character
mode.
passwd [options] set or change your password
paste [options] file paste field(s) onto the lines in file
pr [options] file filter the file and print it on the terminal
ps [options] show status of active processes

Introduction to Unix  1998 University Technology Services, The Ohio State University 129
 Unix Command Summary

TABLE 11.1 Unix Commands

Command/Syntax What it will do

pwd print working (current) directory
rcp [options] hostname remotely copy files from this machine to another machine
rlogin [options] hostname login remotely to another machine
rm [options] file remove (delete) a file or directory (-r recursively deletes the directory
and its contents) (-i prompts before removing files)
rmdir [options] directory remove a directory
rsh [options] hostname remote shell to run on another machine
script file saves everything that appears on the screen to file until exit is executed
sed [options] file stream editor for editing files from a script or from the command line
sort [options] file sort the lines of the file according to the options chosen
source file read commands from the file and execute them in the current shell.
. file source: C shell, .: Bourne shell.

strings [options] file report any sequence of 4 or more printable characters ending in <NL> or
<NULL>. Usually used to search binary files for ASCII strings.
stty [options] set or display terminal control options
tail [options] file display the last few lines (or parts) of a file
tar key[options] [file(s)] tape archiver--refer to man pages for details on creating, listing, and
retrieving from archive files. Tar files can be stored on tape or disk.
tee [options] file copy stdout to one or more files
telnet [host [port]] communicate with another host using telnet protocol
touch [options] [date] file create an empty file, or update the access time of an existing file
tr [options] string1 string2 translate the characters in string1 from stdin into those in string2 in stdout
uncompress file.Z uncompress file.Z and save it as a file
uniq [options] file remove repeated lines in a file
uudecode [file] decode a uuencoded file, recreating the original file
uuencode [file] new_name encode binary file to 7-bit ASCII, useful when sending via email, to be
decoded as new_name at destination
vi [options] file visual, full-screen editor
wc [options] [file(s)] display word (or character or line) count for file(s)
whereis [options] command report the binary, source, and man page locations for the command
named
which command reports the path to the command or the shell alias in use
who or w report who is logged in and what processes are running
zcat file.Z concatenate (list) uncompressed file to screen, leaving file compressed on
disk

130  1998 University Technology Services, The Ohio State University Introduction to Unix
 Highly Recommended

C H A P T E R 12 A Short Unix Bibliography

12.1 Highly Recommended

UNIX for the Impatient, Paul W. Abrahams & Bruce R. Larson (Addison-Wesley Publishing
Company, 1992, ISBN 0-201-55703-7). (A current favorite. Recommended in the CIS Department
for Unix beginners.)
UNIX in a Nutshell for BSD 4.3: A Desktop Quick Reference For Berkeley (O’Reilly & Associates,
Inc., 1990, ISBN 0-937175-20-X). (A handy reference for BSD.)
UNIX in a Nutshell: A Desktop Quick Reference for System V & Solaris 2.0 (O’Reilly & Associates,
Inc., 1992, ISBN 0-56592-001-5). (A handy reference for SysV and Solaris 2.)
The UNIX Programming Environment, Brian W. Kernighan & Rob Pike (Prentice Hall, 1984). (A
classic. For serious folks.)
When You Can’t Find Your UNIX System Administrator, Linda Mui (O’Reilly & Associates, Inc.,
1995, ISBN 1-56592-104-6).
UNIX Power Tools, Jerry Peek, Tim O’Reilly, and Mike Loukides (O’Reilly & Associates, 1993,
ISBN 0-679-79073-X). (Includes a CDROM of useful software for various OSs.)

12.2 Assorted Others

Understanding UNIX: A Conceptual Guide, James R. Groff & Paul N. Weinberg (Que Corporation,
1983).
Exploring the UNIX System, Stephen G. Kochan & Patrick H. Wood (SAMS, a division of
Macmillan Computer Publishing, 1989, ISBN 0-8104-6268-0).
Learning GNU Emacs, Debra Cameron and Bill Rosenblatt (O’Reilly & Associates, 1992, ISBN
0-937175-84-6).
UNIX for Dummies, John R. Levine & Margaret Levine Young (IDG Books Worldwide, Inc., 1993,
ISBN 0-878058-58-4).
A Practical Guide to UNIX System V, Mark G. Sobell (The Benjamin/Cummings Publishing
Company, Inc., 1985, ISBN 0-80-530243-3).
UNIX Primer Plus, Mitchell Waite, Donald Martin, & Stephen Prata, (Howard W. Sams & Co., Inc.,
1983, ISBN 0-672-30194-6).
An Introduction to Berkeley UNIX, Paul Wang, (Wadsworth Publishing Company, 1988).

Introduction to Unix  1998 University Technology Services, The Ohio State University 131
 A Short Unix Bibliography

Unix Shell Programming, Stephen G. Kochan & Patrick H. Wood (Hayden Book Co., 1990, ISBN
0-8104-6309-1).
The Unix C Shell Field Guide, Gail Anderson and Paul Anderson (Prentice Hall, 1986, ISBN
0-13-937468-X).
A Student’s Guide to UNIX, Harley Hahn. (McGraw-Hill, 1993, ISBN 0-07-025511-3).
Tricks of the UNIX Masters, Russell G. Sage (Howard W. Sams & Co., Inc., 1987, ISBN
0-672-22449-6).

132  1998 University Technology Services, The Ohio State University Introduction to Unix