File: grep.info,  Node: Special Backslash Expressions,  Next: Anchoring,  Prev: Character Classes and Bracket Expressions,  Up: Regular Expressions

3.3 Special Backslash Expressions
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The ‘\’ character followed by a special character is a regular
expression that matches the special character.  The ‘\’ character, when
followed by certain ordinary characters, takes a special meaning:

‘\b’
     Match the empty string at the edge of a word.

‘\B’
     Match the empty string provided it's not at the edge of a word.

‘\<’
     Match the empty string at the beginning of a word.

‘\>’
     Match the empty string at the end of a word.

‘\w’
     Match word constituent, it is a synonym for ‘[_[:alnum:]]’.

‘\W’
     Match non-word constituent, it is a synonym for ‘[^_[:alnum:]]’.

‘\s’
     Match whitespace, it is a synonym for ‘[[:space:]]’.

‘\S’
     Match non-whitespace, it is a synonym for ‘[^[:space:]]’.

‘\]’
     Match ‘]’.

‘\}’
     Match ‘}’.

   For example, ‘\brat\b’ matches the separate word ‘rat’, ‘\Brat\B’
matches ‘crate’ but not ‘furry rat’.

   The behavior of ‘grep’ is unspecified if a unescaped backslash is not
followed by a special character, a nonzero digit, or a character in the
above list.  Although ‘grep’ might issue a diagnostic and/or give the
backslash an interpretation now, its behavior may change if the syntax
of regular expressions is extended in future versions.