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man/man1/awk.1
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man/man1/awk.1
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.TH AWK 1
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.SH NAME
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awk \- pattern-directed scanning and processing language
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.SH SYNOPSIS
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.B awk
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[
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||||
.B -F
|
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.I fs
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]
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||||
[
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.B -d
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]
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[
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.BI -mf
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.I n
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]
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[
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.B -mr
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.I n
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]
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[
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.B -safe
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]
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[
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.B -v
|
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.I var=value
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]
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||||
[
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||||
.B -f
|
||||
.I progfile
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||||
|
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||||
.I prog
|
||||
]
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[
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.I file ...
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||||
]
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.SH DESCRIPTION
|
||||
.I Awk
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||||
scans each input
|
||||
.I file
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for lines that match any of a set of patterns specified literally in
|
||||
.I prog
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||||
or in one or more files
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specified as
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||||
.B -f
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.IR progfile .
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With each pattern
|
||||
there can be an associated action that will be performed
|
||||
when a line of a
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||||
.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.
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The file name
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.L -
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means the standard input.
|
||||
Any
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.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;
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any number of
|
||||
.B -v
|
||||
options may be present.
|
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.B -F
|
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.IR fs
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option defines the input field separator to be the regular expression
|
||||
.IR fs .
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.PP
|
||||
An input line is normally made up of fields separated by white space,
|
||||
or by regular expression
|
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.BR FS .
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The fields are denoted
|
||||
.BR $1 ,
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||||
.BR $2 ,
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\&..., while
|
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.B $0
|
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refers to the entire line.
|
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If
|
||||
.BR FS
|
||||
is null, the input line is split into one field per character.
|
||||
.PP
|
||||
To compensate for inadequate implementation of storage management,
|
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the
|
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.B -mr
|
||||
option can be used to set the maximum size of the input record,
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||||
and the
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.B -mf
|
||||
option to set the maximum number of fields.
|
||||
.PP
|
||||
The
|
||||
.B -safe
|
||||
option causes
|
||||
.I awk
|
||||
to run in
|
||||
``safe mode,''
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in which it is not allowed to
|
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run shell commands or open files
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||||
and the environment is not made available
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||||
in the
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.B ENVIRON
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variable.
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.PP
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A pattern-action statement has the form
|
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.IP
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.IB pattern " { " action " }
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.PP
|
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A missing
|
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.BI { " action " }
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means print the line;
|
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a missing pattern always matches.
|
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Pattern-action statements are separated by newlines or semicolons.
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.PP
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An action is a sequence of statements.
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A statement can be one of the following:
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.PP
|
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.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
|
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print\fR [ \fP\fIexpression-list \fP\fR] \fP\fR[ \fP>\fI expression \fP\fR]\fP
|
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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
|
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delete\fI array\fP #\fR delete all elements of array\fP
|
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exit\fR [ \fP\fIexpression \fP\fR]\fP #\fR exit immediately; status is \fP\fIexpression\fP
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.EE
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.DT
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.PP
|
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Statements are terminated by
|
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semicolons, newlines or right braces.
|
||||
An empty
|
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.I expression-list
|
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stands for
|
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.BR $0 .
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String constants are quoted \&\fL"\ "\fR,
|
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with the usual C escapes recognized within.
|
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Expressions take on string or numeric values as appropriate,
|
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and are built using the operators
|
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.B + \- * / % ^
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(exponentiation), and concatenation (indicated by white space).
|
||||
The operators
|
||||
.B
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! ++ \-\- += \-= *= /= %= ^= > >= < <= == != ?:
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are also available in expressions.
|
||||
Variables may be scalars, array elements
|
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(denoted
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.IB x [ i ] )
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or fields.
|
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Variables are initialized to the null string.
|
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Array subscripts may be any string,
|
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not necessarily numeric;
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this allows for a form of associative memory.
|
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Multiple subscripts such as
|
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.B [i,j,k]
|
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are permitted; the constituents are concatenated,
|
||||
separated by the value of
|
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.BR SUBSEP .
|
||||
.PP
|
||||
The
|
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.B print
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statement prints its arguments on the standard output
|
||||
(or on a file if
|
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.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
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statement formats its expression list according to the format
|
||||
(see
|
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.IR fprintf (3)) .
|
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The built-in function
|
||||
.BI close( expr )
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||||
closes the file or pipe
|
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.IR expr .
|
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The built-in function
|
||||
.BI fflush( expr )
|
||||
flushes any buffered output for the file or pipe
|
||||
.IR expr .
|
||||
If
|
||||
.IR expr
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||||
is omitted or is a null string, all open files are flushed.
|
||||
.PP
|
||||
The mathematical functions
|
||||
.BR exp ,
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.BR log ,
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.BR sqrt ,
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.BR sin ,
|
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.BR cos ,
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and
|
||||
.BR atan2
|
||||
are built in.
|
||||
Other built-in functions:
|
||||
.TF length
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.TP
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.B length
|
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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
|
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.B $0
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||||
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
|
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string
|
||||
.TP
|
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.BI substr( s , " m" , " n\fL)
|
||||
the
|
||||
.IR n -character
|
||||
substring of
|
||||
.I s
|
||||
that begins at position
|
||||
.IR m
|
||||
counted from 1.
|
||||
.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.
|
||||
.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,
|
||||
0 for end of file, and \-1 for an error.
|
||||
.PP
|
||||
Patterns are arbitrary Boolean combinations
|
||||
(with
|
||||
.BR "! || &&" )
|
||||
of regular expressions and
|
||||
relational expressions.
|
||||
Regular expressions are as in
|
||||
.IR regexp (7).
|
||||
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 \*9/src/cmd/awk
|
||||
.SH SEE ALSO
|
||||
.IR sed (1),
|
||||
.IR regexp (7),
|
||||
.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.
|
||||
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Reference in a new issue