Extended regular expressions

Extended regular expressions are used in the awk(1) and egrep(1) utilities. Below are the corresponding metacharacters:

*   .   ^   $   [ ]   \  ?   +  |  ( )   { }

The following list describes several important characteristics of metacharacters used in extended regular expressions:

• The first seven metacharacters (*, ., ^, $, [, ], \) have the same meaning that they have in basic regular expressions.
• Bracket expressions work the same as with basic regular expressions.
• Instead of \( and \), extended regular expressions use ( and ); instead of \{ and \), extended regular expressions use { and }. To match (, use \(. To match ), use \). To match {, use \{. To match }, use \}.
• The metacharacters ?, +, and | are new. Their meanings are described in the following table:

  Sample pattern	Description
  dog?	Matches 0 or 1 occurrence of the pattern dog.
  dog+	Matches 1 or more occurrences of the pattern dog.
  dog1|dog2	Matches either dog1 or dog2. The pattern hot dog|hamburger matches either hot dog or hamburger. The pattern [Ss]tor(y|ies) matches Story, story, Stories, and stories.

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