(grep.info.gz) Regular Expressions

 
 3 Regular Expressions
 *********************
 
 A "regular expression" is a pattern that describes a set of strings.
 Regular expressions are constructed analogously to arithmetic
 expressions, by using various operators to combine smaller expressions.
 `grep' understands three different versions of regular expression
 syntax: "basic," (BRE) "extended" (ERE) and "perl".  In GNU `grep',
 there is no difference in available functionality between basic and
 extended syntaxes.  In other implementations, basic regular expressions
 are less powerful.  The following description applies to extended
 regular expressions; differences for basic regular expressions are
 summarized afterwards.  Perl regular expressions give additional
 functionality, and are documented in pcresyntax(3) and pcrepattern(3),
 but may not be available on every system.
(grep.info.gz) Regular Expressions

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