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Regex

2.4 The Backslash Character

The `\' character has one of four different meanings, depending on the context in which you use it and what syntax bits are set (see section 2.1 Syntax Bits). It can: 1) stand for itself, 2) quote the next character, 3) introduce an operator, or 4) do nothing.

1. It stands for itself inside a list (see section 3.6 List Operators ([ ... ] and [^ ... ])) if the syntax bit RE_BACKSLASH_ESCAPE_IN_LISTS is not set. For example, `[\]' would match `\'.

2. It quotes (makes ordinary, if it's special) the next character when you use it either:
   • outside a list,(1) or

   • inside a list and the syntax bit RE_BACKSLASH_ESCAPE_IN_LISTS is set.

3. It introduces an operator when followed by certain ordinary characters--sometimes only when certain syntax bits are set. See the cases RE_BK_PLUS_QM, RE_NO_BK_BRACES, RE_NO_BK_VAR, RE_NO_BK_PARENS, RE_NO_BK_REF in 2.1 Syntax Bits. Also:
   • `\b' represents the match-word-boundary operator (see section 4.1.2 The Match-word-boundary Operator (\b)).

   • `\B' represents the match-within-word operator (see section 4.1.3 The Match-within-word Operator (\B)).

   • `\<' represents the match-beginning-of-word operator
     (see section 4.1.4 The Match-beginning-of-word Operator (\<)).

   • `\>' represents the match-end-of-word operator (see section 4.1.5 The Match-end-of-word Operator (\>)).

   • `\w' represents the match-word-constituent operator (see section 4.1.6 The Match-word-constituent Operator (\w)).

   • `\W' represents the match-non-word-constituent operator (see section 4.1.7 The Match-non-word-constituent Operator (\W)).

   • `\`' represents the match-beginning-of-buffer operator and `\'' represents the match-end-of-buffer operator (see section 4.2 Buffer Operators).

   • If Regex was compiled with the C preprocessor symbol emacs defined, then `\sclass' represents the match-syntactic-class operator and `\Sclass' represents the match-not-syntactic-class operator (see section 5.1 Syntactic Class Operators).

4. In all other cases, Regex ignores `\'. For example, `\n' matches `n'.