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Overview of Actions

An awk program or script consists of a series of rules and function definitions, interspersed. (Functions are described later. See section User-defined Functions.)

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 curly braces (`{' and `}'). Each statement specifies one thing to be done. The statements are separated by newlines or semicolons.

The curly braces around an action must be used even if the action contains only one statement, or even if it contains no statements at all. However, if you omit the action entirely, omit the curly 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

Here are the kinds of statements supported in awk:

The next chapter covers control statements in detail.


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