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grep: The Backslash Character and Special Expressions

 
 3.3 The Backslash Character and Special Expressions
 ===================================================
 
 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:]]’.
 
    For example, ‘\brat\b’ matches the separate word ‘rat’, ‘\Brat\B’
 matches ‘crate’ but not ‘furry rat’.
 

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