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
A regular expression. It matches when the text of the input record fits the regular expression. (See Regular Expressions.)
A single expression. It matches when its value is nonzero (if a number) or non-null (if a string). (See Expressions as Patterns.)
A pair of patterns separated by a comma, specifying a range of records. The range includes both the initial record that matches begpat and the final record that matches endpat. (See Specifying Record Ranges with Patterns.)
Special patterns for you to supply startup or cleanup actions for your
END Special Patterns.)
Special patterns for you to supply startup or cleanup actions to be
done on a per-file basis.
ENDFILE Special Patterns.)
The empty pattern matches every input record. (See The Empty Pattern.)