Nisha Roche
Asst. Prof
Dept of CSE, SJEC
In this chapter
Initial categorization of files
Features of unix filename
Hierarchical structure containing files and directories
Parent child relationship
Significance of home directory and HOME variable
cd and pwd command
mkdir and rmdir
Absolute and relative pathnames
Using ls command
Class Objective
Understand the meaning of a file and its categories
Valid filename
Parent-Child Relationship
The HOME Variable
Pwd
Cd
mkdir/rmdir
Absolute Pathnames
The File
File is a container for storing information
Unix file doesn’t have eof(enf of file) mark
All file attributes are kept in a separate area of the hard
disk, accessible by the kernel
Naming File
In Unix system, a filename can be max of 255
characters.
May or may not have extensions
Can consist of any ASCII Character except the / and
the NULL Character(ASCII Value 0).
Can include control characters as well as unprintable
characters.
Best Practices for filenames
Alphabetic Characters and numerals
The period(.), hyphen(-) and underscore(_)
Never use “ –” at the beginning of a filename.
Eg: -p (shell interprets it as option)
Did you Know?
Unix Does not impose any restrictions on the
extensions, It is the compiler which imposes
restrictions.
Eg: .c (c files), .txt(text files) .sh(shell programs)
A file can have as many dots embedded in its name.
Eg: .a.b.c . , .a.b.c,
Unix is case sensitive
Eg: chap02, CHAP02
Three Categories of files
Ordinary file
All programs that we write belongs to this file
Directory File
Contains files and other directories
Actually it contains file name and a unique number
Device File
All devices and peripherals are represented by files.
Eg: device drivers
Three Categories of files
Ordinary file
Text File
Contain only printable characters
C, Java programs, pearl scripts are text files
Binary File
Contains both printable and unprintable characters
that cover the ASCII range(0 to 255)
Eg: Unix commands and object codes
Directory File
Every directory consists of filename and a unique
number-inode number
Device Files
Device files are found under /dev directory
All devices and peripherals are represented by files.
Eg: device drivers
Class Objective
Parent child relationship
Significance of home directory and HOME variable
cd and pwd command
mkdir and rmdir
Absolute and relative pathnames
Parent Child Relationship-The Unix
File System Tree
The Home and PWD command
The shell variable HOME knows your home directory.
$ echo $ HOME
/home/staff
PWD: Checking your current Directory
$ pwd (present working Directory)
/home/staff
cd: changing the current Directory
Cd command can be used to move around in the file
system.
When used with an argument it changes the current
directory to the directory specified as argument.
Cd command can be used without arguments
mkdir: Making Directories
Directories are created with the mkdir command.
Eg: mkdir patch
mkdir patch dbs doc //Three Directories created.
mkdir rahul rahul/progrs rahul/data //creates the
directory tree.
mkdir rahul/data rahul/progs
rahul ERROR
Possible reasons for failure of directory creation
Directory with a particular name might already
exist
There may be an ordinary file by that name in the
current directory
Permissions set for the current directory doesn’t
permit the creation of files and directories by the
user.
rmdir: REMOVING DIRECTORIES
rmdir ( remove directory) command removes
directories.
rmdir rahul //directory must be empty
To delete directory and subdirectory
rmdir rahul/data rahul/progs rahul
Absolute Pathnames and Relative
Pathnames
Refer class notes
Using . and ..
Refer class notes
Reflection on the previous class
Absolute and relative pathnames
Using . And ..
$PATH
Identify the directory?
Ans: Home directory
The ls command
Used to list all the filenames in the current directory
Can you list the options for $ ls?
-a
-l
-u
-r
-t
Other ls options
Output in Multiple Columns(-x):
Allows to display filenames in multiple columns.
Syntax: ls –x
Other ls options
Identifying Directories and executables (-F):
Used to identify Directories and executable files in
addition to file names.
$ls –Fx
* indicates executable code
/ directory
Other ls options
Showing hidden files (-a)
ls command normally doesn’t show hidden files in a
directory. To view the hidden files in the home
directory –a option can be used.
Syntax:$ls –axF
Other ls options
Listing Directory Contents:
Syntax: $ ls –x directoryname1,directory name2……
$ ls –x helpdir progs
Other ls options
Recursive Listing(-R)
The –R(recursive) option lists all files and
subdirectories in a directory tree.
$ ls –Rx
Chapter 5
Handling Ordinary Files
Topics in this chapter
View text files with cat and more command
Cat to create file
Copy,remove and rename commands.
Count the number of lines , words and characters
Display ASCII octal value of text with od
The display.txt and display1.txt file
originally contains the following information
Output of display.txt
Output of display1.txt
Cat command can be used for the
following purposes
used to Displaying contents of files
$ cat display.txt
Display contents of multiple files:
Displays contents of second file immediately after
displaying content of first file
Cat command can be used for the
following purposes
Used to create new files
cat > foo // blank file foo gets created
$ cat
Cat is a versatile command . It can be used to create,
display, concatenate and append to files.
Cat command can also be used to send the data from
one file to anothe
cat display.txt> display1.txt // if the display1.txt file
already exists then after execution of the above
command the display1.txt content will be overwritten.
$ cat options
There are 2 cat options
1. Displaying Non printing Characters(-v):
Normally used to display text files
When used with –v option displays nonprinting ASCII
characters in the input
Syntax: $ cat -v
$ cat options
2. Numbering Lines(-n): cat –n numbers lines in a
program.
Helps the programmer while debugging
Copy Command
Used to copy files or group of files
Creates a exact duplicate copy with a different file
name
Requires minimum 2 file names.
Predict the output: Assume the
PWD to be USP
$ cp display.txt play.txt
Copy display.txt to play.txt
$ cp display.txt display.txt
error
The $rm command: Remove files
Uses
Used to delete a single file
Used to delete multiple files
Used to delete files and subdirectories
mv command
2 distinct features
It renames a file (directory)
Eg: mv display.txt screen.txt
It moves a group of files to a different directory
mv display.txt discover.txt chap03 kapoor
Here kapoor is a directory
mv: Renaming files
Can be used to rename a directory
mv kumar Rao //Assuming Rao directory doesn’t
exist.
If Rao directory exists then kumar becomes a
subdirectory
-i and R options are available with mv command also
The Pager Program
Paging program, is a computer program used to view
(but not modify) the contents of a text file by moving
down the file one line or one screen at a time.
Not all, pagers allow movement in a file
The Pager Program
2 types of pager programs
more
Allows to move one line at a time but cannot move
backwards
PAGER=more;export PAGER
man ls Set the shell variable PAGER to
use less as its pager and export
it. Then run man command
less
Allows both forward and backwards in text files
PAGER=less;export PAGER
man ls
More: paging output
Man command displays output one page at a time
Unix offers more pager
Linux offers more but less is the standard pager.
Eg more display.txt
----more—(17%)
which means 17% of the document “display.txt” is
shown on screen.
Navigation
f or spacebar to move forward
b to move backward
Repeat factor:
10f //10 pages move ahead
10b //10 pages move backwards
2f // 2 pages move forward
