7.1 Pattern Elements
Patterns in 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 awk patterns:
- A regular expression. It matches when the text of the
input record fits the regular expression.
- A single expression. It matches when its value
is nonzero (if a number) or non-null (if a string).
(See Expression Patterns.)
- 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.
- Special patterns for you to supply startup or cleanup actions for your
- Special patterns for you to supply startup or cleanup actions to be
done on a per file basis.
- The empty pattern matches every input record.