Section A.2. Extended Regular Expressions

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A.2. Extended Regular Expressions

Some utilities such as egrep support an extended set of metacharacters, which are described in Figure A-3.

Figure A-3. Extended regular expression metacharacters.

Metacharacter	Meaning
+	Matches one or more occurrences of the single preceding character.
?	Matches zero or one occurrence of the single preceding character.
| (pipe symbol)	If you place a pipe symbol between two regular expressions, a string that matches either expression will be accepted. In other words, a | acts like an "or" operator.
()	If you place a regular expression in parentheses, you may use the *, +, or ? metacharacters to operate on the entire expression, rather than just a single character.

Figure A-4 lists some examples of full regular expressions, using the example file from Section A.1.1.

Figure A-4. Lines matching extended regular expression patterns.

Pattern	Lines that match
s.*w	Oh you sleepy young heads dream of wonderful things, Beautiful mermaids will swim through the sea, And you will be swimming there too.
s.+w	Oh you sleepy young heads dream of wonderful things, Beautiful mermaids will swim through the sea,
off|will	So turn off the light, Beautiful mermaids will swim through the sea, And you will be swimming there too.
im*ing	And you will be swimming there too.
im?ing	<no matches>