I use awk nearly every day for various data processing tasks. Once in a while, I need to reference the manual. This page is meant to be a concise version of the most important parts of awk so I don’t have to do that as much.

## String Functions

Function Description
gsub(r, s, [t]) substitute s for r globally in $0 or t if provided. Return number of substitutions made. index(s, t) return first position (1-based) of string t in s, or 0 if t is not present. length(s) return number of characters in s. match(s, r) test whether s contains a substring matched by r. Return index (1-based) or 0; sets RSTART and RLENGTH. split(s, a) split s into array a on FS, return number of fields. sprintf(fmt, expr-list) return expr-list formatted according to format string fmt. sub(r, s, [t]) substitute s for the leftmost longest substring of $0 (or t if provided) matched by r, return number of substitutions made.
substr(s, p, [n]) return suffix of s starting at position p (1-based), n number of characters if provided.

## Escape Sequences

Sequence Meaning
\b backspace
\f formfeed
\n newline (line feed)
\r carriage return
\t tab
\ddd octal value ddd, where ddd is 1 to 3 digit between 0 and 7

## Built In Variables

Variable Meaning Default
ARGC Number of command line arguments -
ARGV Array of command line arguments -
FILENAME Name of current input file -
FNR Record number in the current file -
FS Controls the input field separator " "
NF Number of fields in the current record -
NR Number of records read so far -
OFMT Output format for numbers "%.6g"
OFS Output field separator " "
ORS Output record separator \n
RLENGTH length of string matched by match function -
RS Controls the input record separator \n
RSTART start of string matched by match function -
SUBSEP subscript separator \034

## Comparison Operators

Operator Meaning
== equality
!= not equal to
~ matched by
!~ not matched by

## Regular Expression Metacharacters

\, ^, \$, ., [, ], |, (, ), *, +, ?

## User Defined Functions

function yourname(parameter-list,        local variables) {
statements
}


## Truthiness

0 and the empty string "" are considered false, everything else is true. The result from a boolean operator like && will be a numeric 1 if true, 0 if false.