@findex re-builder
@cindex regular expressions, developing
- For convenient interactive development of regular expressions, you
+ For interactive development of regular expressions, you
can use the @kbd{M-x re-builder} command. It provides a convenient
interface for creating regular expressions, by giving immediate visual
feedback in a separate buffer. As you edit the regexp, all its
expression. Thus, @samp{fo*} has a repeating @samp{o}, not a repeating
@samp{fo}. It matches @samp{f}, @samp{fo}, @samp{foo}, and so on.
+@cindex backtracking and regular expressions
The matcher processes a @samp{*} construct by matching, immediately, as
many repetitions as can be found. Then it continues with the rest of
the pattern. If that fails, backtracking occurs, discarding some of the
@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
+If @code{case-fold-search} is non-@code{nil}, @samp{[a-z]} also
+matches upper-case letters. Note that a range like @samp{[a-z]} is
+not affected by the locale's collation sequence, it always represents
+a sequence in @acronym{ASCII} order.
+
+Note also that the usual regexp special characters are not special inside a
character alternative. A completely different set of characters is
special inside character alternatives: @samp{]}, @samp{-} and @samp{^}.
first character. For example, @samp{[]a]} matches @samp{]} or @samp{a}.
To include a @samp{-}, write @samp{-} as the first or last character of
the character alternative, or put it after a range. Thus, @samp{[]-]}
-matches both @samp{]} and @samp{-}.
+matches both @samp{]} and @samp{-}. (As explained below, you cannot
+use @samp{\]} to include a @samp{]} inside a character alternative,
+since @samp{\} is not special there.)
To include @samp{^} in a character alternative, put it anywhere but at
the beginning.
+@c What if it starts with a multibyte and ends with a unibyte?
+@c That doesn't seem to match anything...?
If a range starts with a unibyte character @var{c} and ends with a
multibyte character @var{c2}, the range is divided into two parts: one
-is @samp{@var{c}..?\377}, the other is @samp{@var{c1}..@var{c2}}, where
-@var{c1} is the first character of the charset to which @var{c2}
-belongs.
+spans the unibyte characters @samp{@var{c}..?\377}, the other the
+multibyte characters @samp{@var{c1}..@var{c2}}, where @var{c1} is the
+first character of the charset to which @var{c2} belongs.
A character alternative can also specify named character classes
-(@pxref{Char Classes}). This is a POSIX feature whose syntax is
-@samp{[:@var{class}:]}. Using a character class is equivalent to
-mentioning each of the characters in that class; but the latter is not
-feasible in practice, since some classes include thousands of
-different characters.
+(@pxref{Char Classes}). This is a POSIX feature. For example,
+@samp{[[:ascii:]]} matches any @acronym{ASCII} character.
+Using a character class is equivalent to mentioning each of the
+characters in that class; but the latter is not feasible in practice,
+since some classes include thousands of different characters.
@item @samp{[^ @dots{} ]}
@cindex @samp{^} in regexp
@kindex invalid-regexp
Not every string is a valid regular expression. For example, a string
-that ends inside a character alternative without terminating @samp{]}
+that ends inside a character alternative without a terminating @samp{]}
is invalid, and so is a string that ends with a single @samp{\}. If
an invalid regular expression is passed to any of the search functions,
an @code{invalid-regexp} error is signaled.
regexp constructed by the function @code{sentence-end}.
@xref{Standard Regexps}.)
- First, we show the regexp as a string in Lisp syntax to distinguish
-spaces from tab characters. The string constant begins and ends with a
+ Below, we show first the regexp as a string in Lisp syntax (to
+distinguish spaces from tab characters), and then the result of
+evaluating it. The string constant begins and ends with a
double-quote. @samp{\"} stands for a double-quote as part of the
string, @samp{\\} for a backslash as part of the string, @samp{\t} for a
tab and @samp{\n} for a newline.
-@example
-"[.?!][]\"')@}]*\\($\\| $\\|\t\\|@ @ \\)[ \t\n]*"
-@end example
-
-@noindent
-In contrast, if you evaluate this string, you will see the following:
-
@example
@group
"[.?!][]\"')@}]*\\($\\| $\\|\t\\|@ @ \\)[ \t\n]*"
@end example
@noindent
-In this output, tab and newline appear as themselves.
+In the output, tab and newline appear as themselves.
This regular expression contains four parts in succession and can be
deciphered as follows:
projects / emacs.git / commitdiff