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.TH AWK 1

.SH NAME

awk \- pattern-directed scanning and processing language

.SH SYNOPSIS

.B awk

[

.B -F

.I fs

]

[

.B -d

]

[

.BI -mf

.I n

]

[

.B -mr

.I n

]

[

.B -safe

]

[

.B -v

.I var=value

]

[

.B -f

.I progfile

|

.I prog

]

[

.I file ...

]

.SH DESCRIPTION

.I Awk

scans each input

.I file

for lines that match any of a set of patterns specified literally in

.I prog

or in one or more files

specified as

.B -f

.IR progfile .

With each pattern

there can be an associated action that will be performed

when a line of a

.I file

matches the pattern.

Each line is matched against the

pattern portion of every pattern-action statement;

the associated action is performed for each matched pattern.

The file name 

.L -

means the standard input.

Any

.IR file

of the form

.I var=value

is treated as an assignment, not a file name,

and is executed at the time it would have been opened if it were a file name.

The option

.B -v

followed by

.I var=value

is an assignment to be done before the program

is executed;

any number of

.B -v

options may be present.

.B -F

.IR fs

option defines the input field separator to be the regular expression

.IR fs .

.PP

An input line is normally made up of fields separated by white space,

or by regular expression

.BR FS .

The fields are denoted

.BR $1 ,

.BR $2 ,

\&..., while

.B $0

refers to the entire line.

If

.BR FS

is null, the input line is split into one field per character.

.PP

To compensate for inadequate implementation of storage management,

the 

.B -mr

option can be used to set the maximum size of the input record,

and the

.B -mf

option to set the maximum number of fields.

.PP

The

.B -safe

option causes

.I awk

to run in 

``safe mode,''

in which it is not allowed to 

run shell commands or open files

and the environment is not made available

in the 

.B ENVIRON

variable.

.PP

A pattern-action statement has the form

.IP

.IB pattern " { " action " }

.PP

A missing 

.BI { " action " }

means print the line;

a missing pattern always matches.

Pattern-action statements are separated by newlines or semicolons.

.PP

An action is a sequence of statements.

A statement can be one of the following:

.PP

.EX

.ta \w'\fLdelete array[expression]'u

if(\fI expression \fP)\fI statement \fP\fR[ \fPelse\fI statement \fP\fR]\fP

while(\fI expression \fP)\fI statement\fP

for(\fI expression \fP;\fI expression \fP;\fI expression \fP)\fI statement\fP

for(\fI var \fPin\fI array \fP)\fI statement\fP

do\fI statement \fPwhile(\fI expression \fP)

break

continue

{\fR [\fP\fI statement ... \fP\fR] \fP}

\fIexpression\fP	#\fR commonly\fP\fI var = expression\fP

print\fR [ \fP\fIexpression-list \fP\fR] \fP\fR[ \fP>\fI expression \fP\fR]\fP

printf\fI format \fP\fR[ \fP,\fI expression-list \fP\fR] \fP\fR[ \fP>\fI expression \fP\fR]\fP

return\fR [ \fP\fIexpression \fP\fR]\fP

next	#\fR skip remaining patterns on this input line\fP

nextfile	#\fR skip rest of this file, open next, start at top\fP

delete\fI array\fP[\fI expression \fP]	#\fR delete an array element\fP

delete\fI array\fP	#\fR delete all elements of array\fP

exit\fR [ \fP\fIexpression \fP\fR]\fP	#\fR exit immediately; status is \fP\fIexpression\fP

.EE

.DT

.PP

Statements are terminated by

semicolons, newlines or right braces.

An empty

.I expression-list

stands for

.BR $0 .

String constants are quoted \&\fL"\ "\fR,

with the usual C escapes recognized within.

Expressions take on string or numeric values as appropriate,

and are built using the operators

.B + \- * / % ^

(exponentiation), and concatenation (indicated by white space).

The operators

.B

! ++ \-\- += \-= *= /= %= ^= > >= < <= == != ?:

are also available in expressions.

Variables may be scalars, array elements

(denoted

.IB x  [ i ] )

or fields.

Variables are initialized to the null string.

Array subscripts may be any string,

not necessarily numeric;

this allows for a form of associative memory.

Multiple subscripts such as

.B [i,j,k]

are permitted; the constituents are concatenated,

separated by the value of

.BR SUBSEP .

.PP

The

.B print

statement prints its arguments on the standard output

(or on a file if

.BI > file

or

.BI >> file

is present or on a pipe if

.BI | cmd

is present), separated by the current output field separator,

and terminated by the output record separator.

.I file

and

.I cmd

may be literal names or parenthesized expressions;

identical string values in different statements denote

the same open file.

The

.B printf

statement formats its expression list according to the format

(see

.IR fprintf (2)) .

The built-in function

.BI close( expr )

closes the file or pipe

.IR expr .

The built-in function

.BI fflush( expr )

flushes any buffered output for the file or pipe

.IR expr .

If

.IR expr

is omitted or is a null string, all open files are flushed.

.PP

The mathematical functions

.BR exp ,

.BR log ,

.BR sqrt ,

.BR sin ,

.BR cos ,

and

.BR atan2 

are built in.

Other built-in functions:

.TF length

.TP

.B length

If its argument is a string, the string's length is returned.

If its argument is an array, the number of subscripts in the array is returned.

If no argument, the length of

.B $0

is returned.

.TP

.B rand

random number on (0,1)

.TP

.B srand

sets seed for

.B rand

and returns the previous seed.

.TP

.B int

truncates to an integer value

.TP

.B utf

converts its numerical argument, a character number, to a

.SM UTF

string

.TP

.BI substr( s , " m" , " n\fL)

the

.IR n -character

substring of

.I s

that begins at position

.IR m 

counted from 1.

If

.I n

is omitted, it is taken to be the length of

.I s

from

.IR m .

.TP

.BI index( s , " t" )

the position in

.I s

where the string

.I t

occurs, or 0 if it does not.

.TP

.BI match( s , " r" )

the position in

.I s

where the regular expression

.I r

occurs, or 0 if it does not.

The variables

.B RSTART

and

.B RLENGTH

are set to the position and length of the matched string.

.TP

.BI split( s , " a" , " fs\fL)

splits the string

.I s

into array elements

.IB a [1]\f1,

.IB a [2]\f1,

\&...,

.IB a [ n ]\f1,

and returns

.IR n .

The separation is done with the regular expression

.I fs

or with the field separator

.B FS

if

.I fs

is not given.

An empty string as field separator splits the string

into one array element per character.

.TP

.BI sub( r , " t" , " s\fL)

substitutes

.I t

for the first occurrence of the regular expression

.I r

in the string

.IR s .

If

.I s

is not given,

.B $0

is used.

A

.L &

character in

.I t

will be replaced by the sub-string of

.I s

matched by

.IR r ;

it may be escaped with

.L \e

to substitute a literal

.LR & .

.TP

.B gsub

same as

.B sub

except that all occurrences of the regular expression

are replaced;

.B sub

and

.B gsub

return the number of replacements.

.TP

.BI sprintf( fmt , " expr" , " ...\fL)

the string resulting from formatting

.I expr ...

according to the

.I printf

format

.I fmt

.TP

.BI system( cmd )

executes

.I cmd

and returns its exit status

.TP

.BI tolower( str )

returns a copy of

.I str

with all upper-case characters translated to their

corresponding lower-case equivalents.

.TP

.BI toupper( str )

returns a copy of

.I str

with all lower-case characters translated to their

corresponding upper-case equivalents.

.PD

.PP

The ``function''

.B getline

sets

.B $0

to the next input record from the current input file;

.B getline

.BI < file

sets

.B $0

to the next record from

.IR file .

.B getline

.I x

sets variable

.I x

instead.

Finally,

.IB cmd " | getline

pipes the output of

.I cmd

into

.BR getline ;

each call of

.B getline

returns the next line of output from

.IR cmd .

In all cases,

.B getline

returns 1 for a successful input,

.PP

Patterns are arbitrary Boolean combinations

(with

.BR "! || &&" )

of regular expressions and

relational expressions.

Regular expressions are as in

.IR regexp (6).

Isolated regular expressions

in a pattern apply to the entire line.

Regular expressions may also occur in

relational expressions, using the operators

.BR ~

and

.BR !~ .

.BI / re /

is a constant regular expression;

any string (constant or variable) may be used

as a regular expression, except in the position of an isolated regular expression

in a pattern.

.PP

A pattern may consist of two patterns separated by a comma;

in this case, the action is performed for all lines

from an occurrence of the first pattern

though an occurrence of the second.

.PP

A relational expression is one of the following:

.IP

.I expression matchop regular-expression

.br

.I expression relop expression

.br

.IB expression " in " array-name

.br

.BI ( expr , expr,... ") in " array-name

.PP

where a

.I relop

is any of the six relational operators in C,

and a

.I matchop

is either

.B ~

(matches)

or

.B !~

(does not match).

A conditional is an arithmetic expression,

a relational expression,

or a Boolean combination

of these.

.PP

The special patterns

.B BEGIN

and

.B END

may be used to capture control before the first input line is read

and after the last.

.B BEGIN

and

.B END

do not combine with other patterns.

.PP

Variable names with special meanings:

.TF FILENAME

.TP

.B CONVFMT

conversion format used when converting numbers

(default

.BR "%.6g" )

.TP

.B FS

regular expression used to separate fields; also settable

by option

.BI \-F fs\f1.

.TP

.BR NF

number of fields in the current record

.TP

.B NR

ordinal number of the current record

.TP

.B FNR

ordinal number of the current record in the current file

.TP

.B FILENAME

the name of the current input file

.TP

.B RS

input record separator (default newline)

.TP

.B OFS

output field separator (default blank)

.TP

.B ORS

output record separator (default newline)

.TP

.B OFMT

output format for numbers (default

.BR "%.6g" )

.TP

.B SUBSEP

separates multiple subscripts (default 034)

.TP

.B ARGC

argument count, assignable

.TP

.B ARGV

argument array, assignable;

non-null members are taken as file names

.TP

.B ENVIRON

array of environment variables; subscripts are names.

.PD

.PP

Functions may be defined (at the position of a pattern-action statement) thus:

.IP

.L

function foo(a, b, c) { ...; return x }

.PP

Parameters are passed by value if scalar and by reference if array name;

functions may be called recursively.

Parameters are local to the function; all other variables are global.

Thus local variables may be created by providing excess parameters in

the function definition.

.SH EXAMPLES

.TP

.L

length($0) > 72

Print lines longer than 72 characters.

.TP

.L

{ print $2, $1 }

Print first two fields in opposite order.

.PP

.EX

BEGIN { FS = ",[ \et]*|[ \et]+" }

      { print $2, $1 }

.EE

.ns

.IP

Same, with input fields separated by comma and/or blanks and tabs.

.PP

.EX

	{ s += $1 }

END	{ print "sum is", s, " average is", s/NR }

.EE

.ns

.IP

Add up first column, print sum and average.

.TP

.L

/start/, /stop/

Print all lines between start/stop pairs.

.PP

.EX

BEGIN	{	# Simulate echo(1)

	for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]

	printf "\en"

	exit }

.EE

.SH SOURCE

.B /sys/src/cmd/awk

.SH SEE ALSO

.IR sed (1),

.IR regexp (6),

.br

A. V. Aho, B. W. Kernighan, P. J. Weinberger,

.I

The AWK Programming Language,

Addison-Wesley, 1988.  ISBN 0-201-07981-X

.SH BUGS

There are no explicit conversions between numbers and strings.

To force an expression to be treated as a number add 0 to it;

to force it to be treated as a string concatenate

\&\fL""\fP to it.

.br

The scope rules for variables in functions are a botch;

the syntax is worse.

.br

UTF is not always dealt with correctly,

though

.I awk

does make an attempt to do so.

The

.I split

function with an empty string as final argument now copes

with UTF in the string being split.