GNU Info

(gawk.info)BEGIN/END

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The `BEGIN' and `END' Special Patterns
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   All the patterns described so far are for matching input records.
The `BEGIN' and `END' special patterns are different.  They supply
startup and cleanup actions for `awk' programs.  `BEGIN' and `END'
rules must have actions; there is no default action for these rules
because there is no current record when they run.  `BEGIN' and `END'
rules are often referred to as "`BEGIN' and `END' blocks" by long-time
`awk' programmers.

Using BEGIN/END

How and why to use BEGIN/END rules.

I/O And BEGIN/END

I/O issues in BEGIN/END rules.