glib-regex-syntax.html

最新gtk中文资料集

<tr>
<td align="center">Z</td>
<td>Separator</td>
</tr>
<tr>
<td align="center">Zl</td>
<td>Line separator</td>
</tr>
<tr>
<td align="center">Zp</td>
<td>Paragraph separator</td>
</tr>
<tr>
<td align="center">Zs</td>
<td>Space separator</td>
</tr>
</tbody>
</table></div>
</div>
<br class="table-break"><p>
The special property L&amp; is also supported: it matches a character that has
the Lu, Ll, or Lt property, in other words, a letter that is not classified as
a modifier or "other".
</p>
<p>
The long synonyms for these properties that Perl supports (such as \ep{Letter})
are not supported by GRegex, nor is it permitted to prefix any of these
properties with "Is".
</p>
<p>
No character that is in the Unicode table has the Cn (unassigned) property.
Instead, this property is assumed for any code point that is not in the
Unicode table.
</p>
<p>
Specifying caseless matching does not affect these escape sequences.
For example, \p{Lu} always matches only upper case letters.
</p>
<p>
The \X escape matches any number of Unicode characters that form an
extended Unicode sequence. \X is equivalent to
</p>
<pre class="programlisting">
(?&gt;\PM\pM*)
</pre>
<p>
That is, it matches a character without the "mark" property, followed
by zero or more characters with the "mark" property, and treats the
sequence as an atomic group (see below). Characters with the "mark"
property are typically accents that affect the preceding character.
</p>
<p>
Matching characters by Unicode property is not fast, because GRegex has
to search a structure that contains data for over fifteen thousand
characters. That is why the traditional escape sequences such as \d and
\w do not use Unicode properties.
</p>
</div>
<hr>
<div class="refsect2" lang="en">
<a name="id2814777"></a><h3>Simple assertions</h3>
<p>
The final use of backslash is for certain simple assertions. An
assertion specifies a condition that has to be met at a particular point in
a match, without consuming any characters from the string. The
use of subpatterns for more complicated assertions is described below.
The backslashed assertions are:
</p>
<div class="table">
<a name="id2814790"></a><p class="title"><b>Table&#160;8.&#160;Simple assertions</b></p>
<div class="table-contents"><table summary="Simple assertions" border="1">
<colgroup>
<col align="center">
<col>
</colgroup>
<thead><tr>
<th align="center">Escape</th>
<th>Meaning</th>
</tr></thead>
<tbody>
<tr>
<td align="center">\b</td>
<td>matches at a word boundary</td>
</tr>
<tr>
<td align="center">\B</td>
<td>matches when not at a word boundary</td>
</tr>
<tr>
<td align="center">\A</td>
<td>matches at the start of the string</td>
</tr>
<tr>
<td align="center">\Z</td>
<td>matches at the end of the string or before a newline at the end of the string</td>
</tr>
<tr>
<td align="center">\z</td>
<td>matches only at the end of the string</td>
</tr>
<tr>
<td align="center">\G</td>
<td>matches at first matching position in the string</td>
</tr>
</tbody>
</table></div>
</div>
<br class="table-break"><p>
These assertions may not appear in character classes (but note that \b
has a different meaning, namely the backspace character, inside a
character class).
</p>
<p>
A word boundary is a position in the string where the current
character and the previous character do not both match \w or \W (i.e.
one matches \w and the other matches \W), or the start or end of the
string if the first or last character matches \w, respectively.
</p>
<p>
The \A, \Z, and \z assertions differ from the traditional circumflex
and dollar (described in the next section) in that they only ever match
at the very start and end of the string, whatever options are
set. Thus, they are independent of multiline mode. These three assertions
are not affected by the <code class="varname">G_REGEX_MATCH_NOTBOL</code> or <code class="varname">G_REGEX_MATCH_NOTEOL</code> options,
which affect only the behaviour of the circumflex and dollar metacharacters.
However, if the start_position argument of a matching function is non-zero,
indicating that matching is to start at a point other than the beginning of
the string, \A can never match. The difference between \Z and \z is
that \Z matches before a newline at the end of the string as well at the
very end, whereas \z matches only at the end.
</p>
<p>
The \G assertion is true only when the current matching position is at
the start point of the match, as specified by the start_position argument
to the matching functions. It differs from \A when the value of startoffset is
non-zero.
</p>
<p>
Note, however, that the interpretation of \G, as the start of the
current match, is subtly different from Perl&#8217;s, which defines it as the
end of the previous match. In Perl, these can be different when the
previously matched string was empty.
</p>
<p>
If all the alternatives of a pattern begin with \G, the expression is
anchored to the starting match position, and the "anchored" flag is set
in the compiled regular expression.
</p>
</div>
</div>
<div class="refsect1" lang="en">
<a name="id2814955"></a><h2>Circumflex and dollar</h2>
<p>
Outside a character class, in the default matching mode, the circumflex
character is an assertion that is true only if the current matching
point is at the start of the string. If the start_position argument to
the matching functions is non-zero, circumflex can never match if the
<code class="varname">G_REGEX_MULTILINE</code> option is unset. Inside a character class, circumflex
has an entirely different meaning (see below).
</p>
<p>
Circumflex need not be the first character of the pattern if a number
of alternatives are involved, but it should be the first thing in each
alternative in which it appears if the pattern is ever to match that
branch. If all possible alternatives start with a circumflex, that is,
if the pattern is constrained to match only at the start of the string,
it is said to be an "anchored" pattern. (There are also other
constructs that can cause a pattern to be anchored.)
</p>
<p>
A dollar character is an assertion that is true only if the current
matching point is at the end of the string, or immediately
before a newline at the end of the string (by default). Dollar need not
be the last character of the pattern if a number of alternatives are
involved, but it should be the last item in any branch in which it
appears. Dollar has no special meaning in a character class.
</p>
<p>
The meaning of dollar can be changed so that it matches only at the
very end of the string, by setting the <code class="varname">G_REGEX_DOLLAR_ENDONLY</code> option at
compile time. This does not affect the \Z assertion.
</p>
<p>
The meanings of the circumflex and dollar characters are changed if the
<code class="varname">G_REGEX_MULTILINE</code> option is set. When this is the case,
a circumflex matches immediately after internal newlines as well as at the
start of the string. It does not match after a newline that ends the string.
A dollar matches before any newlines in the string, as well as at the very
end, when <code class="varname">G_REGEX_MULTILINE</code> is set. When newline is
specified as the two-character sequence CRLF, isolated CR and LF characters
do not indicate newlines.
</p>
<p>
For example, the pattern /^abc$/ matches the string "def\nabc" (where
\n represents a newline) in multiline mode, but not otherwise. Consequently,
patterns that are anchored in single line mode because all branches start with
^ are not anchored in multiline mode, and a match for circumflex is possible
when the <code class="varname">start_position</code> argument of a matching function
is non-zero. The <code class="varname">G_REGEX_DOLLAR_ENDONLY</code> option is ignored
if <code class="varname">G_REGEX_MULTILINE</code> is set.
</p>
<p>
Note that the sequences \A, \Z, and \z can be used to match the start and
end of the string in both modes, and if all branches of a pattern start with
\A it is always anchored, whether or not <code class="varname">G_REGEX_MULTILINE</code>
is set.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2815052"></a><h2>Full stop (period, dot)</h2>
<p>
Outside a character class, a dot in the pattern matches any one character
in the string, including a non-printing character, but not (by
default) newline. In UTF-8 a character might be more than one byte long.
</p>
<p>
When a line ending is defined as a single character, dot never matches that
character; when the two-character sequence CRLF is used, dot does not match CR
if it is immediately followed by LF, but otherwise it matches all characters
(including isolated CRs and LFs). When any Unicode line endings are being
recognized, dot does not match CR or LF or any of the other line ending
characters.
</p>
<p>
If the <code class="varname">G_REGEX_DOTALL</code> flag is set, dots match newlines
as well. The handling of dot is entirely independent of the handling of circumflex
and dollar, the only relationship being that they both involve newline
characters. Dot has no special meaning in a character class.
</p>
<p>
The behaviour of dot with regard to newlines can be changed. If the
<code class="varname">G_REGEX_DOTALL</code> option is set, a dot matches any one
character, without exception. If newline is defined as the two-character
sequence CRLF, it takes two dots to match it.
</p>
<p>
The handling of dot is entirely independent of the handling of circumflex and
dollar, the only relationship being that they both involve newlines. Dot has no
special meaning in a character class.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2815103"></a><h2>Matching a single byte</h2>
<p>
Outside a character class, the escape sequence \C matches any one byte,
both in and out of UTF-8 mode. Unlike a dot, it always matches any line
ending characters.
The feature is provided in Perl in order to match individual bytes in
UTF-8 mode. Because it breaks up UTF-8 characters into individual
bytes, what remains in the string may be a malformed UTF-8 string. For
this reason, the \C escape sequence is best avoided.
</p>
<p>
GRegex does not allow \C to appear in lookbehind assertions (described
below), because in UTF-8 mode this would make it impossible to calculate
the length of the lookbehind.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2815126"></a><h2>Square brackets and character classes</h2>
<p>
An opening square bracket introduces a character class, terminated by a
closing square bracket. A closing square bracket on its own is not special. If a closing square bracket is required as a member of the class,
it should be the first data character in the class (after an initial
circumflex, if present) or escaped with a backslash.
</p>
<p>
A character class matches a single character in the string.  A matched character
must be in the set of characters defined by the class, unless the first
character in the class definition is a circumflex, in which case the
string character must not be in the set defined by the class. If a
circumflex is actually required as a member of the class, ensure it is
not the first character, or escape it with a backslash.
</p>
<p>
For example, the character class [aeiou] matches any lower case vowel,
while [^aeiou] matches any character that is not a lower case vowel.
Note that a circumflex is just a convenient notation for specifying the
characters that are in the class by enumerating those that are not. A
class that starts with a circumflex is not an assertion: it still consumes
a character from the string, and therefore it fails if the current pointer
is at the end of the string.
</p>
<p>
In UTF-8 mode, characters with values greater than 255 can be included
in a class as a literal string of bytes, or by using the \x{ escaping
mechanism.
</p>
<p>
When caseless matching is set, any letters in a class represent both
their upper case and lower case versions, so for example, a caseless
[aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not
match "A", whereas a caseful version would.
</p>
<p>
Characters that might indicate line breaks are never treated
in any special way when matching character classes, whatever line-ending
sequence is in use, and whatever setting of the <code class="varname">G_REGEX_DOTALL</code>
and <code class="varname">G_REGEX_MULTILINE</code> options is used. A class such as [^a]
always matches one of these characters.
</p>
<p>
The minus (hyphen) character can be used to specify a range of characters in
a character class. For example, [d-m] matches any letter
between d and m, inclusive. If a minus character is required in a
class, it must be escaped with a backslash or appear in a position
where it cannot be interpreted as indicating a range, typically as the
first or last character in the class.
</p>
<p>
It is not possible to have the literal character "]" as the end character
of a range. A pattern such as [W-]46] is interpreted as a class of
two characters ("W" and "-") followed by a literal string "46]", so it
would match "W46]" or "-46]". However, if the "]" is escaped with a
backslash it is interpreted as the end of range, so [W-\]46] is interpreted
as a class containing a range followed by two other characters.
The octal or hexadecimal representation of "]" can also be used to end
a range.
</p>
<p>
Ranges operate in the collating sequence of character values. They can
also be used for characters specified numerically, for example
[\000-\037]. In UTF-8 mode, ranges can include characters whose values
are greater than 255, for example [\x{100}-\x{2ff}].
</p>
<p>
The character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear
in a character class, and add the characters that they match to the
class. For example, [\dABCDEF] matches any hexadecimal digit. A
circumflex can conveniently be used with the upper case character types to
specify a more restricted set of characters than the matching lower
case type. For example, the class [^\W_] matches any letter or digit,
but not underscore.
</p>
<p>
The only metacharacters that are recognized in character classes are
backslash, hyphen (only where it can be interpreted as specifying a
range), circumflex (only at the start), opening square bracket (only
when it can be interpreted as introducing a POSIX class name - see the
next section), and the terminating closing square bracket. However,
escaping other non-alphanumeric characters does no harm.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2815241"></a><h2>Posix character classes</h2>
<p>
GRegex supports the POSIX notation for character classes. This uses names
enclosed by [: and :] within the enclosing square brackets. For example,
</p>
<pre class="programlisting">
[01[:alpha:]%]
</pre>
<p>
matches "0", "1", any alphabetic character, or "%". The supported class
names are
</p>
<div class="table">
<a name="id2815262"></a><p class="title"><b>Table&#160;9.&#160;Posix classes</b></p>
<div class="table-contents"><table summary="Posix classes" border="1">
<colgroup>
<col align="center">
<col>
</colgroup>
<thead><tr>
<th align="center">Name</th>
<th>Meaning</th>
</tr></thead>
<tbody>
<tr>
<td align="center">alnum</td>
<td>letters and digits</td>
</tr>
<tr>
<td align="center">alpha</td>
<td>letters</td>
</tr>
<tr>
<td align="center">ascii</td>