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Patterns in @command{awk} control the execution of rules--a rule is
executed when its pattern matches the current input record.
The following is a summary of the types of patterns in @command{awk}:
/regular expression/
-
A regular expression. It matches when the text of the
input record fits the regular expression.
(See section Regular Expressions.)
expression
-
A single expression. It matches when its value
is nonzero (if a number) or non-null (if a string).
(See section Expressions as Patterns.)
pat1, pat2
-
A pair of patterns separated by a comma, specifying a range of records.
The range includes both the initial record that matches pat1 and
the final record that matches pat2.
(See section Specifying Record Ranges with Patterns.)
BEGIN
-
END
-
Special patterns for you to supply startup or cleanup actions for your
@command{awk} program.
(See section The
BEGIN and END Special Patterns.)
empty
-
The empty pattern matches every input record.
(See section The Empty Pattern.)
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