gawk: Action Overview
7.3 Actions
===========
An 'awk' program or script consists of a series of rules and function
definitions interspersed. (Functions are described later.
User-defined.) A rule contains a pattern and an action, either of
which (but not both) may be omitted. The purpose of the "action" is to
tell 'awk' what to do once a match for the pattern is found. Thus, in
outline, an 'awk' program generally looks like this:
[PATTERN] '{ ACTION }'
PATTERN ['{ ACTION }']
...
'function NAME(ARGS) { ... }'
...
An action consists of one or more 'awk' "statements", enclosed in
braces ('{...}'). Each statement specifies one thing to do. The
statements are separated by newlines or semicolons. The braces around
an action must be used even if the action contains only one statement,
or if it contains no statements at all. However, if you omit the action
entirely, omit the braces as well. An omitted action is equivalent to
'{ print $0 }':
/foo/ { } match 'foo', do nothing -- empty action
/foo/ match 'foo', print the record -- omitted action
The following types of statements are supported in 'awk':
Expressions
Call functions or assign values to variables (Expressions).
Executing this kind of statement simply computes the value of the
expression. This is useful when the expression has side effects
(Assignment Ops).
Control statements
Specify the control flow of 'awk' programs. The 'awk' language
gives you C-like constructs ('if', 'for', 'while', and 'do') as
well as a few special ones (Statements).
Compound statements
Enclose one or more statements in braces. A compound statement is
used in order to put several statements together in the body of an
'if', 'while', 'do', or 'for' statement.
Input statements
Use the 'getline' command (Getline). Also supplied in
'awk' are the 'next' statement (Next Statement) and the
'nextfile' statement (Nextfile Statement).
Output statements
Such as 'print' and 'printf'. Printing.
Deletion statements
For deleting array elements. Delete.