Manual browser: awk(1)

AWK(1)

General Commands Manual

AWK(1)

NAME

awk — pattern-directed scanning and processing language

SYNOPSIS

awk	[-F fs] [-v var=value] [-safe] [-d[N]] [prog \| -f filename] file ...

awk	-version

DESCRIPTION

awk is the Bell Labs' implementation of the AWK programming language as described in the The AWK Programming Language by A. V. Aho, B. W. Kernighan, and P. J. Weinberger.

awk scans each input file for lines that match any of a set of patterns specified literally in prog or in one or more files specified as -f filename. With each pattern there can be an associated action that will be performed when a line of a 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. Any file of the form var=value is treated as an assignment, not a filename, and is executed at the time it would have been opened if it were a filename.

The options are as follows:

An input line is normally made up of fields separated by white space, or by regular expression FS. The fields are denoted $1, $2, ..., while $0 refers to the entire line. If FS is null, the input line is split into one field per character.

A pattern-action statement has the form

pattern { action }

A missing { action } means print the line; a missing pattern always matches. Pattern-action statements are separated by newlines or semicolons.

An action is a sequence of statements. Statements are terminated by semicolons, newlines or right braces. An empty expression-list stands for $0. String constants are quoted " ", with the usual C escapes recognized within. Expressions take on string or numeric values as appropriate, and are built using the Operators (see next subsection). 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. Multiple subscripts such as [i,j,k] are permitted; the constituents are concatenated, separated by the value of SUBSEP.

Operators

awk operators, in order of decreasing precedence, are:

Control Statements

The control statements are as follows:

if ( expression ) statement [else statement]
while ( expression ) statement
for ( expression ; expression ; expression ) statement
for ( var in array ) statement
do statement while ( expression )
break
continue
delete array [expression]
delete array
exit [expression]: expression
return [expression]
{ [statement ...] }

I/O Statements

The input/output statements are as follows:

Mathematical and Numeric Functions

AWK has the following mathematical and numerical functions built-in:

String Functions

AWK has the following string functions built-in:

Time Functions

This awk provides the following two functions for obtaining time stamps and formatting them:

Other built-in functions

Patterns

Patterns are arbitrary Boolean combinations (with ! || &&) of regular expressions and relational expressions. Regular expressions are as in 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 !~. / 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.

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.

A relational expression is one of the following:

where a relop is any of the six relational operators in C, and a matchop is either ~ (matches) or !~ (does not match). A conditional is an arithmetic expression, a relational expression, or a Boolean combination of these.

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.

Built-in Variables

Variable names with special meanings:

ARGC: argument count, assignable
ARGV: argument array, assignable; non-null members are taken as filenames
CONVFMT: conversion format used when converting numbers (default “%.6g”)
ENVIRON: array of environment variables; subscripts are names.
FILENAME: the name of the current input file
FNR: ordinal number of the current record in the current file
FS: regular expression used to separate fields; also settable by option -F fs.
NF: number of fields in the current record
NR: ordinal number of the current record
OFMT: output format for numbers (default “%.6g” )
OFS: output field separator (default blank)
ORS: output record separator (default newline)
RS: input record separator (default newline)
RSTART: Position of the first character matched by match(); 0 if not match.
RLENGTH: Length of the string matched by match(); -1 if no match.
SUBSEP: separates multiple subscripts (default 034)

Functions

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

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

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.

EXAMPLES

HISTORY

nawk has been the default system awk since NetBSD 2.0, replacing the previously used GNU awk.

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.

The scope rules for variables in functions are a botch; the syntax is worse.

April 6, 2015

NetBSD 7.0

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