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(Regexps): More accurately describe which characters are special in

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which situations.  Recommend _not_ to quote `]' or `-' when they are
not special.
This commit is contained in:
Luc Teirlinck 2006-03-09 02:03:20 +00:00
parent fc1d338658
commit a955f5752e
1 changed files with 15 additions and 5 deletions
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20
man/search.texi
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@ -498,11 +498,13 @@ elisp, The Emacs Lisp Reference Manual}.
special constructs and the rest are @dfn{ordinary}. An ordinary
character is a simple regular expression which matches that same
character and nothing else. The special characters are @samp{$},
@samp{^}, @samp{.}, @samp{*}, @samp{+}, @samp{?}, @samp{[}, @samp{]} and
@samp{\}. Any other character appearing in a regular expression is
ordinary, unless a @samp{\} precedes it. (When you use regular
expressions in a Lisp program, each @samp{\} must be doubled, see the
example near the end of this section.)
@samp{^}, @samp{.}, @samp{*}, @samp{+}, @samp{?}, @samp{[}, and
@samp{\}. The character @samp{]} is special if it ends a character
alternative (see later). The character @samp{-} is special inside a
character alternative. Any other character appearing in a regular
expression is ordinary, unless a @samp{\} precedes it. (When you use
regular expressions in a Lisp program, each @samp{\} must be doubled,
see the example near the end of this section.)
For example, @samp{f} is not a special character, so it is ordinary, and
therefore @samp{f} is a regular expression that matches the string
@ -682,6 +684,14 @@ no preceding expression on which the @samp{*} can act. It is poor practice
to depend on this behavior; it is better to quote the special character anyway,
regardless of where it appears.
As a @samp{\} is not special inside a character alternative, it can
never remove the special meaning of @samp{-} or @samp{]}. So you
should not quote these characters when they have no special meaning
either. This would not clarify anything, since backslashes can
legitimately precede these characters where they @emph{have} special
meaning, as in @code{[^\]} (@code{"[^\\]"} for Lisp string syntax),
which matches any single character except a backslash.
@node Regexp Backslash
@section Backslash in Regular Expressions