From 65401ee3fefe38cb3a8a350a17f8b0a3a4ccb579 Mon Sep 17 00:00:00 2001 From: Chong Yidong Date: Fri, 28 Jan 2011 13:03:30 -0500 Subject: * search.texi (Regexps): Copyedits. Mention character classes (Bug#7809). --- doc/emacs/ChangeLog | 3 ++ doc/emacs/search.texi | 113 +++++++++++++++++++++++++------------------------- 2 files changed, 60 insertions(+), 56 deletions(-) diff --git a/doc/emacs/ChangeLog b/doc/emacs/ChangeLog index 4d4d38c2c5..f3c6afc3fa 100644 --- a/doc/emacs/ChangeLog +++ b/doc/emacs/ChangeLog @@ -1,5 +1,8 @@ 2011-01-28 Chong Yidong + * search.texi (Regexps): Copyedits. Mention character classes + (Bug#7809). + * files.texi (File Aliases): Restore explanatory text from Eli Zaretskii, accidentally removed in 2011-01-08 commit. diff --git a/doc/emacs/search.texi b/doc/emacs/search.texi index cd63a562d6..e2ecb4a238 100644 --- a/doc/emacs/search.texi +++ b/doc/emacs/search.texi @@ -546,21 +546,20 @@ Search}. @cindex syntax of regexps This manual describes regular expression features that users -typically want to use. There are additional features that are -mainly used in Lisp programs; see @ref{Regular Expressions,,, -elisp, The Emacs Lisp Reference Manual}. +typically use. @xref{Regular Expressions,,, elisp, The Emacs Lisp +Reference Manual}, for additional features used mainly in Lisp +programs. Regular expressions have a syntax in which a few characters are 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{$}, -@samp{^}, @samp{.}, @samp{*}, @samp{+}, @samp{?}, @samp{[}, and -@samp{\}. The character @samp{]} is special if it ends a character -alternative (see later). The character @samp{-} is special inside a -character alternative. Any other character appearing in a regular -expression is ordinary, unless a @samp{\} precedes it. (When you use -regular expressions in a Lisp program, each @samp{\} must be doubled, -see the example near the end of this section.) +character matches that same character and nothing else. The special +characters are @samp{$^.*+?[\}. 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 @@ -570,28 +569,27 @@ only @samp{o}. (When case distinctions are being ignored, these regexps also match @samp{F} and @samp{O}, but we consider this a generalization of ``the same string,'' rather than an exception.) - Any two regular expressions @var{a} and @var{b} can be concatenated. The -result is a regular expression which matches a string if @var{a} matches -some amount of the beginning of that string and @var{b} matches the rest of -the string.@refill - - As a simple example, we can concatenate the regular expressions @samp{f} -and @samp{o} to get the regular expression @samp{fo}, which matches only -the string @samp{fo}. Still trivial. To do something nontrivial, you -need to use one of the special characters. Here is a list of them. + Any two regular expressions @var{a} and @var{b} can be concatenated. +The result is a regular expression which matches a string if @var{a} +matches some amount of the beginning of that string and @var{b} +matches the rest of the string. For example, concatenating the +regular expressions @samp{f} and @samp{o} gives the regular expression +@samp{fo}, which matches only the string @samp{fo}. Still trivial. +To do something nontrivial, you need to use one of the special +characters. Here is a list of them. @table @asis @item @kbd{.}@: @r{(Period)} -is a special character that matches any single character except a newline. -Using concatenation, we can make regular expressions like @samp{a.b}, which -matches any three-character string that begins with @samp{a} and ends with -@samp{b}.@refill +is a special character that matches any single character except a +newline. For example, the regular expressions @samp{a.b} matches any +three-character string that begins with @samp{a} and ends with +@samp{b}. @item @kbd{*} is not a construct by itself; it is a postfix operator that means to -match the preceding regular expression repetitively as many times as -possible. Thus, @samp{o*} matches any number of @samp{o}s (including no -@samp{o}s). +match the preceding regular expression repetitively any number of +times, as many times as possible. Thus, @samp{o*} matches any number +of @samp{o}s, including no @samp{o}s. @samp{*} always applies to the @emph{smallest} possible preceding expression. Thus, @samp{fo*} has a repeating @samp{o}, not a repeating @@ -610,22 +608,21 @@ With this choice, the rest of the regexp matches successfully.@refill @item @kbd{+} is a postfix operator, similar to @samp{*} except that it must match -the preceding expression at least once. So, for example, @samp{ca+r} -matches the strings @samp{car} and @samp{caaaar} but not the string -@samp{cr}, whereas @samp{ca*r} matches all three strings. +the preceding expression at least once. Thus, @samp{ca+r} matches the +strings @samp{car} and @samp{caaaar} but not the string @samp{cr}, +whereas @samp{ca*r} matches all three strings. @item @kbd{?} -is a postfix operator, similar to @samp{*} except that it can match the -preceding expression either once or not at all. For example, -@samp{ca?r} matches @samp{car} or @samp{cr}; nothing else. +is a postfix operator, similar to @samp{*} except that it can match +the preceding expression either once or not at all. Thus, @samp{ca?r} +matches @samp{car} or @samp{cr}, and nothing else. @item @kbd{*?}, @kbd{+?}, @kbd{??} @cindex non-greedy regexp matching -are non-greedy variants of the operators above. The normal operators -@samp{*}, @samp{+}, @samp{?} are @dfn{greedy} in that they match as -much as they can, as long as the overall regexp can still match. With -a following @samp{?}, they are non-greedy: they will match as little -as possible. +are non-@dfn{greedy} variants of the operators above. The normal +operators @samp{*}, @samp{+}, @samp{?} match as much as they can, as +long as the overall regexp can still match. With a following +@samp{?}, they will match as little as possible. Thus, both @samp{ab*} and @samp{ab*?} can match the string @samp{a} and the string @samp{abbbb}; but if you try to match them both against @@ -641,29 +638,30 @@ a newline, it matches the whole string. Since it @emph{can} match starting at the first @samp{a}, it does. @item @kbd{\@{@var{n}\@}} -is a postfix operator that specifies repetition @var{n} times---that -is, the preceding regular expression must match exactly @var{n} times -in a row. For example, @samp{x\@{4\@}} matches the string @samp{xxxx} -and nothing else. +is a postfix operator specifying @var{n} repetitions---that is, the +preceding regular expression must match exactly @var{n} times in a +row. For example, @samp{x\@{4\@}} matches the string @samp{xxxx} and +nothing else. @item @kbd{\@{@var{n},@var{m}\@}} -is a postfix operator that specifies repetition between @var{n} and -@var{m} times---that is, the preceding regular expression must match -at least @var{n} times, but no more than @var{m} times. If @var{m} is +is a postfix operator specifying between @var{n} and @var{m} +repetitions---that is, the preceding regular expression must match at +least @var{n} times, but no more than @var{m} times. If @var{m} is omitted, then there is no upper limit, but the preceding regular expression must match at least @var{n} times.@* @samp{\@{0,1\@}} is equivalent to @samp{?}. @* @samp{\@{0,\@}} is equivalent to @samp{*}. @* @samp{\@{1,\@}} is equivalent to @samp{+}. @item @kbd{[ @dots{} ]} -is a @dfn{character set}, which begins with @samp{[} and is terminated -by @samp{]}. In the simplest case, the characters between the two -brackets are what this set can match. +is a @dfn{character set}, beginning with @samp{[} and terminated by +@samp{]}. -Thus, @samp{[ad]} matches either one @samp{a} or one @samp{d}, and -@samp{[ad]*} matches any string composed of just @samp{a}s and @samp{d}s -(including the empty string), from which it follows that @samp{c[ad]*r} -matches @samp{cr}, @samp{car}, @samp{cdr}, @samp{caddaar}, etc. +In the simplest case, the characters between the two brackets are what +this set can match. Thus, @samp{[ad]} matches either one @samp{a} or +one @samp{d}, and @samp{[ad]*} matches any string composed of just +@samp{a}s and @samp{d}s (including the empty string). It follows that +@samp{c[ad]*r} matches @samp{cr}, @samp{car}, @samp{cdr}, +@samp{caddaar}, etc. You can also include character ranges in a character set, by writing the starting and ending characters with a @samp{-} between them. Thus, @@ -672,9 +670,12 @@ intermixed freely with individual characters, as in @samp{[a-z$%.]}, which matches any lower-case @acronym{ASCII} letter or @samp{$}, @samp{%} or period. -Note that the usual regexp special characters are not special inside a -character set. A completely different set of special characters exists -inside character sets: @samp{]}, @samp{-} and @samp{^}. +You can also include certain special @dfn{character classes} in a +character set. A @samp{[:} and balancing @samp{:]} enclose a +character class inside a character alternative. For instance, +@samp{[[:alnum:]]} matches any letter or digit. @xref{Char Classes,,, +elisp, The Emacs Lisp Reference Manual}, for a list of character +classes. To include a @samp{]} in a character set, you must make it the first character. For example, @samp{[]a]} matches @samp{]} or @samp{a}. To -- cgit v1.2.3