.so mnx.mac

.TH AWK 1x

.CD "awk \(en pattern matching language"

.SX "awk \fIrules\fR [\fIfile\fR] ...

.FL "\fR(none)"

.EX "awk rules input" "Process \fIinput\fR according to \fIrules\fR"

.EX "awk rules \(en >out" "Input from terminal, output to \fIout\fR"

.PP

AWK is a programming language devised by Aho, Weinberger, and Kernighan

at Bell Labs (hence the name).

\fIAwk\fR programs search files for

specific patterns and performs \*(OQactions\*(CQ for every occurrence

of these patterns. The patterns can be \*(OQregular expressions\*(CQ

as used in the \fIed\fR editor. The actions are expressed

using a subset of the C language.

.PP

The patterns and actions are usually placed in a \*(OQrules\*(CQ file

whose name must be the first argument in the command line,

preceded by the flag \fB\(enf\fR. Otherwise, the first argument on the

command line is taken to be a string containing the rules

themselves. All other arguments are taken to be the names of text

files on which the rules are to be applied, with \fB\(en\fR being the

standard input. To take rules from the standard input, use \fB\(enf \(en\fR.

.PP

The command:

.HS

.Cx "awk rules prog.\d\s+2*\s0\u"

.HS

would read the patterns and actions rules from the file \fIrules\fR

and apply them to all the arguments.

.PP

The general format of a rules file is:

.HS

~~~<pattern> { <action> }

~~~<pattern> { <action> }

~~~...

.HS

There may be any number of these <pattern> { <action> }

sequences in the rules file. \fIAwk\fR reads a line of input from

the current input file and applies every <pattern> { <action> }

in sequence to the line.

.PP

If the <pattern> corresponding to any { <action> } is missing,

the action is applied to every line of input. The default

{ <action> } is to print the matched input line.

.SS "Patterns"

.PP

The <pattern>s may consist of any valid C expression. If the

<pattern> consists of two expressions separated by a comma, it

is taken to be a range and the <action> is performed on all

lines of input that match the range. <pattern>s may contain

\*(OQregular expressions\*(CQ delimited by an @ symbol. Regular

expressions can be thought of as a generalized \*(OQwildcard\*(CQ

string matching mechanism, similar to that used by many

operating systems to specify file names. Regular expressions

may contain any of the following characters:

.HS

.in +0.75i

.ta +0.5i

.ti -0.5i

x An ordinary character

.ti -0.5i

\\ The backslash quotes any character

.ti -0.5i

^ A circumflex at the beginning of an expr matches the beginning of a line.

.ti -0.5i

$ A dollar-sign at the end of an expression matches the end of a line.

.ti -0.5i

\&. A period matches any single character except newline.

.ti -0.5i

* An expression followed by an asterisk matches zero or more occurrences

of that expression: \*(OQfo*\*(CQ matches \*(OQf\*(CQ, \*(OQfo\*(CQ, \*(OQfoo\*(CQ, \*(OQfooo\*(CQ, etc.

.ti -0.5i

+ An expression followed by a plus sign matches one or more occurrences

of that expression: \*(OQfo+\*(CQ matches \*(OQfo\*(CQ, \*(OQfoo\*(CQ, \*(OQfooo\*(CQ, etc.

.ti -0.5i

[] A string enclosed in square brackets matches any single character in that

string, but no others. If the first character in the string is a circumflex, the

expression matches any character except newline and the characters in the

string. For example, \*(OQ[xyz]\*(CQ matches \*(OQxx\*(CQ and \*(OQzyx\*(CQ, while

\*(OQ[^xyz]\*(CQ matches \*(OQabc\*(CQ but not \*(OQaxb\*(CQ. A range of characters may be

specified by two characters separated by \*(OQ-\*(CQ.

.in -0.75i

.SS "Actions"

.PP

Actions are expressed as a subset of the C language. All

variables are global and default to int's if not formally

declared.

Only char's and int's and pointers and arrays of

char and int are allowed. \fIAwk\fR allows only decimal integer

constants to be used\(emno hex (0xnn) or octal (0nn). String

and character constants may contain all of the special C

escapes (\\n, \\r, etc.).

.PP

\fIAwk\fR supports the \*(OQif\*(CQ, \*(OQelse\*(CQ,

\*(OQwhile\*(CQ and \*(OQbreak\*(CQ flow of

control constructs, which behave exactly as in C.

.PP

Also supported are the following unary and binary operators,

listed in order from highest to lowest precedence:

.HS

.ta 0.25i 1.75i 3.0i

.nf

\fB Operator Type Associativity\fR

() [] unary left to right

.tr ~~

! ~ ++ \(en\(en \(en * & unary right to left

.tr ~

* / % binary left to right

+ \(en binary left to right

<< >> binary left to right

< <= > >= binary left to right

== != binary left to right

& binary left to right

^ binary left to right

| binary left to right

&& binary left to right

|| binary left to right

= binary right to left

.fi

.HS

Comments are introduced by a '#' symbol and are terminated by

the first newline character. The standard \*(OQ/*\*(CQ and \*(OQ*/\*(CQ

comment delimiters are not supported and will result in a

syntax error.

.SP 0.5

.SS "Fields"

.SP 0.5

.PP

When \fIawk\fR reads a line from the current input file, the

record is automatically separated into \*(OQfields.\*(CQ A field is

simply a string of consecutive characters delimited by either

the beginning or end of line, or a \*(OQfield separator\*(CQ character.

Initially, the field separators are the space and tab character.

The special unary operator '$' is used to reference one of the

fields in the current input record (line). The fields are

numbered sequentially starting at 1. The expression \*(OQ$0\*(CQ

references the entire input line.

.PP

Similarly, the \*(OQrecord separator\*(CQ is used to determine the end

of an input \*(OQline,\*(CQ initially the newline character. The field

and record separators may be changed programatically by one of

the actions and will remain in effect until changed again.

.PP

Multiple (up to 10) field separators are allowed at a time, but

only one record separator.

.PP

Fields behave exactly like strings; and can be used in the same

context as a character array. These \*(OQarrays\*(CQ can be considered

to have been declared as:

.SP 0.15

.HS

~~~~~char ($n)[ 128 ];

.HS

.SP 0.15

In other words, they are 128 bytes long. Notice that the

parentheses are necessary because the operators [] and $

associate from right to left; without them, the statement

would have parsed as:

.HS

.SP 0.15

~~~~~char $(1[ 128 ]);

.HS

.SP 0.15

which is obviously ridiculous.

.PP

If the contents of one of these field arrays is altered, the

\*(OQ$0\*(CQ field will reflect this change. For example, this

expression:

.HS

.SP 0.15

~~~~~*$4 = 'A';

.HS

.SP 0.15

will change the first character of the fourth field to an upper-

case letter 'A'. Then, when the following input line:

.HS

.SP 0.15

~~~~~120 PRINT "Name address Zip"

.SP 0.15

.HS

is processed, it would be printed as:

.HS

.SP 0.15

~~~~~120 PRINT "Name Address Zip"

.HS

.SP 0.15

Fields may also be modified with the strcpy() function (see

below). For example, the expression:

.HS

~~~~~strcpy( $4, "Addr." );

.HS

applied to the same line above would yield:

.HS

~~~~~120 PRINT "Name Addr. Zip"

.HS

.SS "Predefined Variables"

.PP

The following variables are pre-defined:

.HS

.in +1.5i

.ta +1.25i

.ti -1.25i

FS Field separator (see below).

.ti -1.25i

RS Record separator (see below also).

.ti -1.25i

NF Number of fields in current input record (line).

.ti -1.25i

NR Number of records processed thus far.

.ti -1.25i

FILENAME Name of current input file.

.ti -1.25i

BEGIN A special <pattern> that matches the beginning of input text.

.ti -1.25i

END A special <pattern> that matches the end of input text.

.in -1.5i

.HS

\fIAwk\fR also provides some useful built-in functions for string

manipulation and printing:

.HS

.in +1.5i

.ta +1.25i

.ti -1.25i

print(arg) Simple printing of strings only, terminated by '\\n'.

.ti -1.25i

printf(arg...) Exactly the printf() function from C.

.ti -1.25i

getline() Reads the next record and returns 0 on end of file.

.ti -1.25i

nextfile() Closes the current input file and begins processing the next file

.ti -1.25i

strlen(s) Returns the length of its string argument.

.ti -1.25i

strcpy(s,t) Copies the string \*(OQt\*(CQ to the string \*(OQs\*(CQ.

.ti -1.25i

strcmp(s,t) Compares the \*(OQs\*(CQ to \*(OQt\*(CQ and returns 0 if they match.

.ti -1.25i

toupper(c) Returns its character argument converted to upper-case.

.ti -1.25i

tolower(c) Returns its character argument converted to lower-case.

.ti -1.25i

match(s,@re@) Compares the string \*(OQs\*(CQ to the regular expression \*(OQre\*(CQ and

returns the number of matches found (zero if none).

.in -1.5i

.SS "Authors"

.PP

\fIAwk\fR was written by Saeko Hirabauashi and Kouichi Hirabayashi.