Awk Patterns

The core syntax of awk(1p) is pattern { action }. This page describes patterns.

Contents

Regular Expressions

Regular expressions are essential to awk(1p). They are a builtin type and are expressed as strings delimited by forward slashes (/).

An entire record can be matched against a regular expression as:

/^[0-9]+ / { print $2 }

A variable or field can be matched against a regular expression as:

if ($1 ~ /^[0-9]+$/) { print $2 }

The special patterns BEGIN and END are for initialization and clean-up actions.

To initialize a variable that will be referenced in a program, try:

BEGIN { ansi_reset="\033[0m"; }

To count the number of records (i.e. lines) in a file, try:

END { print NR }

An empty pattern matches every line. This can be written in one of two ways:

{ print "No pattern at all" }
// { print "Blank regexp pattern" }