(grep) Regular Expressions

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 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.
 

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* Fundamental Structure
* Character Classes and Bracket Expressions
* The Backslash Character and Special Expressions
* Anchoring
* Back-references and Subexpressions
* Basic vs Extended
 

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