(gawk.info)Action Overview

Overview of Actions
===================

   An `awk' program or script consists of a series of rules and
function definitions, interspersed.  (Functions are described later.
Note: 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':

   * Expressions, which can call functions or assign values to variables
     (Note: Expressions.).  Executing this kind of statement simply
     computes the value of the expression.  This is useful when the
     expression has side effects (*note Assignment Expressions:
     Assignment Ops.).

   * Control statements, which 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 (Note:
     Control Statements in Actions.).

   * Compound statements, which consist of one or more statements
     enclosed in curly 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, using the `getline' command (Note: Explicit
     Input with `getline'.), the `next' statement (Note: The
     `next' Statement.), and the `nextfile' statement
     (Note: The `nextfile' Statement.).

   * Output statements, `print' and `printf'.  *Note Printing Output:
     Printing.

   * Deletion statements, for deleting array elements.  Note: The
     `delete' Statement.