b525355729
Note: this backs out a number of changes we've made to awk because they aren't upstream, but are on the vendor branch. Those will be reapplied. svn makes it needlessly difficult to know which ones, but at least r315426, r301289, and maybe r301691, though there may be others too. None of these are critical, so bisecting through this point is safe for all but awk regression tests :).
566 lines
11 KiB
Groff
566 lines
11 KiB
Groff
.de EX
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.nf
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.ft CW
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..
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.de EE
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.br
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.fi
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.ft 1
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..
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.TH AWK 1
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.CT 1 files prog_other
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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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.BI \-F
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.I fs
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]
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[
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.BI \-v
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.I var=value
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]
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[
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.I 'prog'
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.BI \-f
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.I progfile
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]
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[
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.I file ...
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]
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.SH DESCRIPTION
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.I Awk
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scans each input
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.I file
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for lines that match any of a set of patterns specified literally in
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.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
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there can be an associated action that will be performed
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when a line of a
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.I file
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matches the pattern.
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Each line is matched against the
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pattern portion of every pattern-action statement;
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the associated action is performed for each matched pattern.
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The file name
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.B \-
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means the standard input.
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Any
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.I file
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of the form
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.I var=value
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is treated as an assignment, not a filename,
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and is executed at the time it would have been opened if it were a filename.
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The option
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.B \-v
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followed by
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.I var=value
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is an assignment to be done before
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.I prog
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is executed;
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any number of
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.B \-v
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options may be present.
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The
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.B \-F
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.I fs
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option defines the input field separator to be the regular expression
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.IR fs .
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.PP
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An input line is normally made up of fields separated by white space,
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or by the regular expression
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.BR FS .
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The fields are denoted
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.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
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.BR FS
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is null, the input line is split into one field per character.
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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
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.ta \w'\f(CWdelete array[expression]\fR'u
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.RS
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.nf
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.ft CW
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if(\fI expression \fP)\fI statement \fP\fR[ \fPelse\fI statement \fP\fR]\fP
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while(\fI expression \fP)\fI statement\fP
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for(\fI expression \fP;\fI expression \fP;\fI expression \fP)\fI statement\fP
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for(\fI var \fPin\fI array \fP)\fI statement\fP
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do\fI statement \fPwhile(\fI expression \fP)
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break
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continue
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{\fR [\fP\fI statement ... \fP\fR] \fP}
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\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
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return\fR [ \fP\fIexpression \fP\fR]\fP
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next #\fR skip remaining patterns on this input line\fP
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nextfile #\fR skip rest of this file, open next, start at top\fP
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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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.fi
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.RE
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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.
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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 \&\f(CW"\ "\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).
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The operators
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.B
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! ++ \-\- += \-= *= /= %= ^= > >= < <= == != ?:
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are also available in expressions.
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Variables may be scalars, array elements
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(denoted
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.IB x [ i ] \fR)
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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,
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separated by the value of
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.BR SUBSEP .
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.PP
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The
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.B print
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statement prints its arguments on the standard output
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(or on a file if
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.BI > " file
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or
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.BI >> " file
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is present or on a pipe if
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.BI | " cmd
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is present), separated by the current output field separator,
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and terminated by the output record separator.
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.I file
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and
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.I cmd
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may be literal names or parenthesized expressions;
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identical string values in different statements denote
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the same open file.
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The
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.B printf
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statement formats its expression list according to the
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.I format
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(see
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.IR printf (3)).
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The built-in function
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.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
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.BI fflush( expr )
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flushes any buffered output for the file or pipe
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.IR expr .
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.PP
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The mathematical functions
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.BR atan2 ,
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.BR cos ,
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.BR exp ,
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.BR log ,
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.BR sin ,
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and
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.B sqrt
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are built in.
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Other built-in functions:
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.TF length
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.TP
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.B length
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the length of its argument
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taken as a string,
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number of elements in an array for an array argument,
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or length of
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.B $0
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if no argument.
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.TP
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.B rand
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random number on [0,1)
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.TP
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.B srand
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sets seed for
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.B rand
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and returns the previous seed.
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.TP
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.B int
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truncates to an integer value
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.TP
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\fBsubstr(\fIs\fB, \fIm\fR [\fB, \fIn\^\fR]\fB)\fR
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the
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.IR n -character
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substring of
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.I s
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that begins at position
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.I m
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counted from 1.
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If no
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.IR m ,
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use the rest of the string
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.I
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.TP
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.BI index( s , " t" )
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the position in
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.I s
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where the string
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.I t
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occurs, or 0 if it does not.
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.TP
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.BI match( s , " r" )
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the position in
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.I s
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where the regular expression
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.I r
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occurs, or 0 if it does not.
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The variables
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.B RSTART
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and
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.B RLENGTH
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are set to the position and length of the matched string.
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.TP
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\fBsplit(\fIs\fB, \fIa \fR[\fB, \fIfs\^\fR]\fB)\fR
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splits the string
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.I s
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into array elements
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.IB a [1] \fR,
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.IB a [2] \fR,
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\&...,
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.IB a [ n ] \fR,
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and returns
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.IR n .
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The separation is done with the regular expression
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.I fs
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or with the field separator
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.B FS
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if
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.I fs
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is not given.
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An empty string as field separator splits the string
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into one array element per character.
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.TP
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\fBsub(\fIr\fB, \fIt \fR[, \fIs\^\fR]\fB)
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substitutes
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.I t
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for the first occurrence of the regular expression
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.I r
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in the string
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.IR s .
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If
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.I s
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is not given,
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.B $0
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is used.
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.TP
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\fBgsub(\fIr\fB, \fIt \fR[, \fIs\^\fR]\fB)
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same as
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.B sub
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except that all occurrences of the regular expression
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are replaced;
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.B sub
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and
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.B gsub
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return the number of replacements.
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.TP
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.BI sprintf( fmt , " expr" , " ...\fB)
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the string resulting from formatting
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.I expr ...
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according to the
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.IR printf (3)
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format
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.IR fmt .
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.TP
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.BI system( cmd )
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executes
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.I cmd
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and returns its exit status. This will be \-1 upon error,
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.IR cmd 's
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exit status upon a normal exit,
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256 +
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.I sig
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upon death-by-signal, where
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.I sig
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is the number of the murdering signal,
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or 512 +
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.I sig
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if there was a core dump.
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.TP
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.BI tolower( str )
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returns a copy of
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.I str
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with all upper-case characters translated to their
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corresponding lower-case equivalents.
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.TP
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.BI toupper( str )
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returns a copy of
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.I str
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with all lower-case characters translated to their
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corresponding upper-case equivalents.
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.PD
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.PP
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The ``function''
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.B getline
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sets
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.B $0
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to the next input record from the current input file;
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.B getline
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.BI < " file
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sets
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.B $0
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to the next record from
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.IR file .
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.B getline
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.I x
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sets variable
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.I x
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instead.
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Finally,
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.IB cmd " | getline
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pipes the output of
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.I cmd
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into
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.BR getline ;
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each call of
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.B getline
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returns the next line of output from
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.IR cmd .
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In all cases,
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.B getline
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returns 1 for a successful input,
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0 for end of file, and \-1 for an error.
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.PP
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Patterns are arbitrary Boolean combinations
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(with
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.BR "! || &&" )
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of regular expressions and
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relational expressions.
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Regular expressions are as in
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.IR egrep (1)
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except numeric quantifiers are not supported beyond the basic
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.B +
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and
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.B ?
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for quantities \&\f(CW"0 or 1"\fP and \&\f(CW"1 or more"\fP
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respectively.
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Isolated regular expressions
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in a pattern apply to the entire line.
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Regular expressions may also occur in
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relational expressions, using the operators
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.B ~
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and
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.BR !~ .
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.BI / re /
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is a constant regular expression;
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any string (constant or variable) may be used
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as a regular expression, except in the position of an isolated regular expression
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in a pattern.
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.PP
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A pattern may consist of two patterns separated by a comma;
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in this case, the action is performed for all lines
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from an occurrence of the first pattern
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though an occurrence of the second.
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.PP
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A relational expression is one of the following:
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.IP
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.I expression matchop regular-expression
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.br
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.I expression relop expression
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.br
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.IB expression " in " array-name
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.br
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.BI ( expr , expr,... ") in " array-name
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.PP
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where a
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.I relop
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is any of the six relational operators in C,
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and a
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.I matchop
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is either
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.B ~
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(matches)
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or
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.B !~
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(does not match).
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A conditional is an arithmetic expression,
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a relational expression,
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or a Boolean combination
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of these.
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.PP
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The special patterns
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.B BEGIN
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and
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.B END
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may be used to capture control before the first input line is read
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and after the last.
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.B BEGIN
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and
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.B END
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do not combine with other patterns.
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They may appear multiple times in a program and execute
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in the order they are read by
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.IR awk .
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.PP
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Variable names with special meanings:
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.TF FILENAME
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.TP
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.B ARGC
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argument count, assignable.
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.TP
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.B ARGV
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argument array, assignable;
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non-null members are taken as filenames.
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.TP
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.B CONVFMT
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conversion format used when converting numbers
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(default
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.BR "%.6g" ).
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.TP
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.B ENVIRON
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array of environment variables; subscripts are names.
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.TP
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.B FILENAME
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the name of the current input file.
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.TP
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.B FNR
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ordinal number of the current record in the current file.
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.TP
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.B FS
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regular expression used to separate fields; also settable
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by option
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.BI \-F fs\fR.
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.TP
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.BR NF
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number of fields in the current record.
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.TP
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.B NR
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ordinal number of the current record.
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.TP
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.B OFMT
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output format for numbers (default
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.BR "%.6g" ).
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.TP
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.B OFS
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|
output field separator (default space).
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.TP
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.B ORS
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|
output record separator (default newline).
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.TP
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.B RLENGTH
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the length of a string matched by
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.BR match .
|
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.TP
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.B RS
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|
input record separator (default newline).
|
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.TP
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.B RSTART
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|
the start position of a string matched by
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.BR match .
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.TP
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.B SUBSEP
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separates multiple subscripts (default 034).
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.PD
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.PP
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|
Functions may be defined (at the position of a pattern-action statement) thus:
|
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.IP
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.B
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function foo(a, b, c) { ...; return x }
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.PP
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Parameters are passed by value if scalar and by reference if array name;
|
|
functions may be called recursively.
|
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Parameters are local to the function; all other variables are global.
|
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Thus local variables may be created by providing excess parameters in
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the function definition.
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.SH EXAMPLES
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.TP
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.EX
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length($0) > 72
|
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.EE
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Print lines longer than 72 characters.
|
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.TP
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|
.EX
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{ print $2, $1 }
|
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.EE
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|
Print first two fields in opposite order.
|
|
.PP
|
|
.EX
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BEGIN { FS = ",[ \et]*|[ \et]+" }
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{ print $2, $1 }
|
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.EE
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|
.ns
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|
.IP
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|
Same, with input fields separated by comma and/or spaces and tabs.
|
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.PP
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|
.EX
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.nf
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{ s += $1 }
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END { print "sum is", s, " average is", s/NR }
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.fi
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.EE
|
|
.ns
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|
.IP
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|
Add up first column, print sum and average.
|
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.TP
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.EX
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/start/, /stop/
|
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.EE
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|
Print all lines between start/stop pairs.
|
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.PP
|
|
.EX
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.nf
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|
BEGIN { # Simulate echo(1)
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for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]
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printf "\en"
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exit }
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.fi
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.EE
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|
.SH SEE ALSO
|
|
.IR grep (1),
|
|
.IR lex (1),
|
|
.IR sed (1)
|
|
.br
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|
A. V. Aho, B. W. Kernighan, P. J. Weinberger,
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.IR "The AWK Programming Language" ,
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Addison-Wesley, 1988. ISBN 0-201-07981-X.
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.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;
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to force it to be treated as a string concatenate
|
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\&\f(CW""\fP to it.
|
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.br
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|
The scope rules for variables in functions are a botch;
|
|
the syntax is worse.
|
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.br
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|
Only eight-bit characters sets are handled correctly.
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