V8/usr/man/man1/awk.1

.TH AWK 1 
.SH NAME
awk \- pattern-directed scanning and processing language
.SH SYNOPSIS
.B awk
[
.BI \-F s
]
[ prog ] [ file ] ...
.SH DESCRIPTION
.I Awk
scans each input
.I file
for lines that match any of a set of patterns specified literally in
.IR prog
or in a file
specified as
.B \-f
.IR file .
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 `\-' means the standard input.
.PP
An input line is made up of fields separated by white space.
(This default can be changed by using FS,
.IR "vide infra" ".)"
The fields are denoted $1, $2, ... ;
$0 refers to the entire line.
.PP
A pattern-action statement has the form
.PP
	pattern { action }
.PP
A missing { action } means print the line;
a missing pattern always matches.
.PP
An action is a sequence of statements.
A statement can be one of the following:
.PP
.nf
	if ( conditional ) statement [ else statement ]
	while ( conditional ) statement
	for ( expression ; conditional ; expression ) statement
	for ( var in array ) statement
	break
	continue
	{ [ statement ] ... }
	expression	# commonly variable = expression
	print [ expression-list ] [ >expression ]
	printf format [ , expression-list ] [ >expression ]
	next		# skip remaining patterns on this input line 
	exit [expr]	# skip the rest of the input; exit status is expr
.fi
.PP
Statements are terminated by
semicolons, newlines or right braces.
An empty expression-list stands for the whole line.
Expressions take on string or numeric values as appropriate,
and are built using the operators
+, \-, *, /, %, ^ (exponentiation), and concatenation (indicated by a blank).
The C operators ++, \-\-, +=, \-=, *=, /=, %= and ^=
are also available in expressions.
Variables may be scalars, array elements
(denoted
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.
String constants are quoted "...".
.PP
The 
.I print
statement prints its arguments on the standard output
(or on a file if 
.I >file
is present or on a pipe if
.I \(orcmd
is present), separated by the current output field separator,
and terminated by the output record separator.
The
.I printf
statement formats its expression list according to the format
(see
.IR printf (3)).
The function
.I close
closes the file or pipe named as its argument.
.PP
The built-in function
.I length
returns the length of its argument
taken as a string,
or of the whole line if no argument.
There are also built-in functions
.IR exp ,
.IR log ,
.IR sqrt ,
.IR sin ,
.IR cos ,
.IR atan2 ,
.I rand
(returns a random number on (0,1)),
.IR srand
(sets seed for
.IR rand ),
and
.IR int
(truncates its argument to an integer).
.IR substr(s,\ m,\ n)
returns the 
.IR n -character
substring of
.I s
that begins at position
.IR m .
.I index(s,\ t)
returns the position in
.I s
where
.I t
occurs, or 0 if it does not.
The function
.I split(s,\ a,\ fs)
splits the string
.I s
into array elements
.IR a[1] ,
.IR a[2] ,
\&...,
.IR a[n] ,
and returns
.IR n .
The separation is done with the regular expression
.I fs
or with the field separator FS
if
.I fs
is not given.
.PP
The function
.I sub(r,\ t,\ s)
substitutes
.I t
for the first occurrence of the regular expression
.I r
in the string
.IR s .
If
.I s
is not given,
$0 is used.
The function
.I gsub
is the same except that all occurrences of the regular expression
are replaced.
.I Sub
and
.I gsub
return the number of replacements.
.PP
The function
.IR sprintf(fmt,\ expr,\ expr,\ ...)
formats the expressions
according to the
.IR printf (3)
format given by
.I fmt
and returns the resulting string.
.PP
The function
.I system(cmd)
executes
.I cmd
and returns its exit status
The function
.I getline
sets $0 to the next input record from the current input file;
.I getline
.I <file
sets $0 to the next record from
.IR file .
.I getline
.I x
sets variable
.I x
instead.
Finally,
.IR cmd \(or getline
pipes the input of
.I cmd
into
.IR getline ;
each call of
.I getline
returns the next line of output from
.IR cmd .
In all cases,
.I getline
returns 1 for a successful input,
0 for end of file, and \-1 for an error.
.PP
Patterns are arbitrary Boolean combinations
(!, \(or\(or, &&, and parentheses) of 
regular expressions and
relational expressions.
Regular expressions are as in
.IR egrep (1).
Isolated regular expressions
in a pattern apply to the entire line.
Regular expressions may also occur in
relational expressions, using the operators ~ and !~.
.I /re/
is a constant regular expression;
in addition, 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
between an occurrence of the first pattern
and the next occurrence of the second, inclusive.
.PP
.nf
A relational expression is one of the following:
.PP
.nf
	expression matchop regular-expression
	expression relop expression
.PP
.fi
where a relop is any of the six relational operators in C,
and a matchop is either ~ (for contains)
or !~ (for does not contain).
A conditional is an arithmetic expression,
a relational expression,
or a Boolean combination
of these.
.PP
The special patterns
BEGIN
and
END
may be used to capture control before the first input line is read
and after the last.
BEGIN and END do not combine with other patterns.
.PP
A regular expression
.I r
may be used to separate fields,
by assigning to the variable FS
or by means of the
.BI \-F s
option.
.PP
Other variable names with special meanings
include NF, the number of fields in the current record;
NR, the ordinal number of the current record;
FNR, the ordinal number of the current record in the current file;
FILENAME, the name of the current input file;
RS, the input record separator (default newline);
OFS, the output field separator (default blank);
ORS, the output record separator (default newline);
OFMT, the output format for numbers (default "%.6g");
ARGC, the argument count;
and
ARGV, the argument array.
ARGC and the ARGV array may be altered;
non-null members are taken as filenames.
.PP
Functions may be defined (at the position of a pattern-action statement) as
.nf
	func foo(a, b, c) {...}
.fi
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.
The
.I return
statement may be used to return a value.
.PP
.SH EXAMPLES
.PP
Print lines longer than 72 characters:
.PP
.nf
	length > 72
.fi
.PP
Print first two fields in opposite order:
.PP
.nf
	{ print $2, $1 }
.fi
.PP
Same, with input fields separated by comma and/or blanks and tabs:
.nf
	BEGIN { FS = ",[ \et]*\(or[ \et]+" }
		{ print $2, $1 }
.PP
Add up first column, print sum and average:
.PP
.nf
		{ s += $1 }
	END	{ print "sum is", s, " average is", s/NR }
.fi
.PP
Print all lines between start/stop pairs:
.PP
.nf
	/start/, /stop/
.fi
.PP
Simulate
.IR echo (1):
.PP
.nf
	BEGIN {
		for (i = 1; i < ARGC; i++)
			printf "%s ", ARGV[i]
		printf "\en"
		exit
	}
.fi
.SH SEE ALSO
lex(1), sed(1), sno(1)
.br
A. V. Aho, B. W. Kernighan, P. J. Weinberger,
.I
Awk \- a pattern scanning and processing language: user's manual
.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 ""
to it.
.PP
The scope rules for variables in functions are a botch.