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< a name = "boost_regex.syntax.perl_syntax" > < / a > < a href = "perl_syntax.html" title = "Perl Regular Expression Syntax" > Perl Regular Expression
Syntax< / a >
< / h3 > < / div > < / div > < / div >
< a name = "boost_regex.syntax.perl_syntax.synopsis" > < / a > < h4 >
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< a name = "id497765" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.synopsis" > Synopsis< / a >
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< / h4 >
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< p >
The Perl regular expression syntax is based on that used by the programming
language Perl . Perl regular expressions are the default behavior in Boost.Regex
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or you can pass the flag < code class = "computeroutput" > < span class = "identifier" > perl< / span > < / code >
to the < a href = "../ref/basic_regex.html" title = "basic_regex" > < code class = "computeroutput" > < span class = "identifier" > basic_regex< / span > < / code > < / a >
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constructor, for example:
< / p >
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< pre class = "programlisting" > < span class = "comment" > // e1 is a case sensitive Perl regular expression:
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< / span > < span class = "comment" > // since Perl is the default option there's no need to explicitly specify the syntax used here:
< / span > < span class = "identifier" > boost< / span > < span class = "special" > ::< / span > < span class = "identifier" > regex< / span > < span class = "identifier" > e1< / span > < span class = "special" > (< / span > < span class = "identifier" > my_expression< / span > < span class = "special" > );< / span >
< span class = "comment" > // e2 a case insensitive Perl regular expression:
< / span > < span class = "identifier" > boost< / span > < span class = "special" > ::< / span > < span class = "identifier" > regex< / span > < span class = "identifier" > e2< / span > < span class = "special" > (< / span > < span class = "identifier" > my_expression< / span > < span class = "special" > ,< / span > < span class = "identifier" > boost< / span > < span class = "special" > ::< / span > < span class = "identifier" > regex< / span > < span class = "special" > ::< / span > < span class = "identifier" > perl< / span > < span class = "special" > |< / span > < span class = "identifier" > boost< / span > < span class = "special" > ::< / span > < span class = "identifier" > regex< / span > < span class = "special" > ::< / span > < span class = "identifier" > icase< / span > < span class = "special" > );< / span >
< / pre >
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< a name = "boost_regex.syntax.perl_syntax.perl_regular_expression_syntax" > < / a > < h4 >
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< a name = "id497986" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.perl_regular_expression_syntax" > Perl
Regular Expression Syntax< / a >
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< / h4 >
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< p >
In Perl regular expressions, all characters match themselves except for the
following special characters:
< / p >
< pre class = "programlisting" > .[{()\*+?|^$< / pre >
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< a name = "boost_regex.syntax.perl_syntax.wildcard" > < / a > < h5 >
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< a name = "id498024" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.wildcard" > Wildcard< / a >
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< / h5 >
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< p >
The single character '.' when used outside of a character set will match
any single character except:
< / p >
< div class = "itemizedlist" > < ul type = "disc" >
< li >
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The NULL character when the < a href = "../ref/match_flag_type.html" title = "match_flag_type" > flag
< code class = "computeroutput" > < span class = "identifier" > match_no_dot_null< / span > < / code > < / a >
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is passed to the matching algorithms.
< / li >
< li >
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The newline character when the < a href = "../ref/match_flag_type.html" title = "match_flag_type" > flag
< code class = "computeroutput" > < span class = "identifier" > match_not_dot_newline< / span > < / code > < / a >
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is passed to the matching algorithms.
< / li >
< / ul > < / div >
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< a name = "boost_regex.syntax.perl_syntax.anchors" > < / a > < h5 >
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< a name = "id498105" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.anchors" > Anchors< / a >
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< / h5 >
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< p >
A '^' character shall match the start of a line.
< / p >
< p >
A '$' character shall match the end of a line.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.marked_sub_expressions" > < / a > < h5 >
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< a name = "id498139" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.marked_sub_expressions" > Marked
sub-expressions< / a >
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< / h5 >
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< p >
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A section beginning < code class = "computeroutput" > < span class = "special" > (< / span > < / code > and ending
< code class = "computeroutput" > < span class = "special" > )< / span > < / code > acts as a marked sub-expression.
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Whatever matched the sub-expression is split out in a separate field by the
matching algorithms. Marked sub-expressions can also repeated, or referred
to by a back-reference.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.non_marking_grouping" > < / a > < h5 >
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< a name = "id498194" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.non_marking_grouping" > Non-marking
grouping< / a >
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< / h5 >
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< p >
A marked sub-expression is useful to lexically group part of a regular expression,
but has the side-effect of spitting out an extra field in the result. As
an alternative you can lexically group part of a regular expression, without
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generating a marked sub-expression by using < code class = "computeroutput" > < span class = "special" > (?:< / span > < / code >
and < code class = "computeroutput" > < span class = "special" > )< / span > < / code > , for example < code class = "computeroutput" > < span class = "special" > (?:< / span > < span class = "identifier" > ab< / span > < span class = "special" > )+< / span > < / code >
will repeat < code class = "computeroutput" > < span class = "identifier" > ab< / span > < / code > without splitting
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out any separate sub-expressions.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.repeats" > < / a > < h5 >
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< a name = "id498283" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.repeats" > Repeats< / a >
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< / h5 >
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< p >
Any atom (a single character, a marked sub-expression, or a character class)
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can be repeated with the < code class = "computeroutput" > < span class = "special" > *< / span > < / code > ,
< code class = "computeroutput" > < span class = "special" > +< / span > < / code > , < code class = "computeroutput" > < span class = "special" > ?< / span > < / code > ,
and < code class = "computeroutput" > < span class = "special" > {}< / span > < / code > operators.
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< / p >
< p >
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The < code class = "computeroutput" > < span class = "special" > *< / span > < / code > operator will match the
preceding atom zero or more times, for example the expression < code class = "computeroutput" > < span class = "identifier" > a< / span > < span class = "special" > *< / span > < span class = "identifier" > b< / span > < / code >
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will match any of the following:
< / p >
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< pre class = "programlisting" > < span class = "identifier" > b< / span >
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< span class = "identifier" > ab< / span >
< span class = "identifier" > aaaaaaaab< / span >
< / pre >
< p >
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The < code class = "computeroutput" > < span class = "special" > +< / span > < / code > operator will match the
preceding atom one or more times, for example the expression < code class = "computeroutput" > < span class = "identifier" > a< / span > < span class = "special" > +< / span > < span class = "identifier" > b< / span > < / code >
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will match any of the following:
< / p >
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< pre class = "programlisting" > < span class = "identifier" > ab< / span >
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< span class = "identifier" > aaaaaaaab< / span >
< / pre >
< p >
But will not match:
< / p >
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< pre class = "programlisting" > < span class = "identifier" > b< / span >
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< / pre >
< p >
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The < code class = "computeroutput" > < span class = "special" > ?< / span > < / code > operator will match the
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preceding atom zero or one times, for example the expression ca?b will match
any of the following:
< / p >
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< pre class = "programlisting" > < span class = "identifier" > cb< / span >
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< span class = "identifier" > cab< / span >
< / pre >
< p >
But will not match:
< / p >
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< pre class = "programlisting" > < span class = "identifier" > caab< / span >
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< / pre >
< p >
An atom can also be repeated with a bounded repeat:
< / p >
< p >
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< code class = "computeroutput" > < span class = "identifier" > a< / span > < span class = "special" > {< / span > < span class = "identifier" > n< / span > < span class = "special" > }< / span > < / code > Matches
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'a' repeated exactly n times.
< / p >
< p >
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< code class = "computeroutput" > < span class = "identifier" > a< / span > < span class = "special" > {< / span > < span class = "identifier" > n< / span > < span class = "special" > ,}< / span > < / code > Matches
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'a' repeated n or more times.
< / p >
< p >
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< code class = "computeroutput" > < span class = "identifier" > a< / span > < span class = "special" > {< / span > < span class = "identifier" > n< / span > < span class = "special" > ,< / span > < span class = "identifier" > m< / span > < span class = "special" > }< / span > < / code > Matches 'a' repeated between n and m times
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inclusive.
< / p >
< p >
For example:
< / p >
< pre class = "programlisting" > ^a{2,3}$< / pre >
< p >
Will match either of:
< / p >
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< pre class = "programlisting" > < span class = "identifier" > aa< / span >
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< span class = "identifier" > aaa< / span >
< / pre >
< p >
But neither of:
< / p >
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< pre class = "programlisting" > < span class = "identifier" > a< / span >
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< span class = "identifier" > aaaa< / span >
< / pre >
< p >
It is an error to use a repeat operator, if the preceding construct can not
be repeated, for example:
< / p >
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< pre class = "programlisting" > < span class = "identifier" > a< / span > < span class = "special" > (*)< / span >
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< / pre >
< p >
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Will raise an error, as there is nothing for the < code class = "computeroutput" > < span class = "special" > *< / span > < / code >
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operator to be applied to.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.non_greedy_repeats" > < / a > < h5 >
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< a name = "id498756" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.non_greedy_repeats" > Non greedy
repeats< / a >
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< / h5 >
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< p >
The normal repeat operators are "greedy", that is to say they will
consume as much input as possible. There are non-greedy versions available
that will consume as little input as possible while still producing a match.
< / p >
< p >
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< code class = "computeroutput" > < span class = "special" > *?< / span > < / code > Matches the previous atom
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zero or more times, while consuming as little input as possible.
< / p >
< p >
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< code class = "computeroutput" > < span class = "special" > +?< / span > < / code > Matches the previous atom
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one or more times, while consuming as little input as possible.
< / p >
< p >
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< code class = "computeroutput" > < span class = "special" > ??< / span > < / code > Matches the previous atom
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zero or one times, while consuming as little input as possible.
< / p >
< p >
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< code class = "computeroutput" > < span class = "special" > {< / span > < span class = "identifier" > n< / span > < span class = "special" > ,}?< / span > < / code > Matches the previous atom n or more times,
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while consuming as little input as possible.
< / p >
< p >
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< code class = "computeroutput" > < span class = "special" > {< / span > < span class = "identifier" > n< / span > < span class = "special" > ,< / span > < span class = "identifier" > m< / span > < span class = "special" > }?< / span > < / code >
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Matches the previous atom between n and m times, while consuming as little
input as possible.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.back_references" > < / a > < h5 >
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< a name = "id498897" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.back_references" > Back references< / a >
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< / h5 >
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< p >
An escape character followed by a digit < span class = "emphasis" > < em > n< / em > < / span > , where < span class = "emphasis" > < em > n< / em > < / span >
is in the range 1-9, matches the same string that was matched by sub-expression
< span class = "emphasis" > < em > n< / em > < / span > . For example the expression:
< / p >
< pre class = "programlisting" > ^(a*).*\1$< / pre >
< p >
Will match the string:
< / p >
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< pre class = "programlisting" > < span class = "identifier" > aaabbaaa< / span >
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< / pre >
< p >
But not the string:
< / p >
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< pre class = "programlisting" > < span class = "identifier" > aaabba< / span >
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< / pre >
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< a name = "boost_regex.syntax.perl_syntax.alternation" > < / a > < h5 >
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< a name = "id498980" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.alternation" > Alternation< / a >
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< / h5 >
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< p >
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The < code class = "computeroutput" > < span class = "special" > |< / span > < / code > operator will match either
of its arguments, so for example: < code class = "computeroutput" > < span class = "identifier" > abc< / span > < span class = "special" > |< / span > < span class = "identifier" > def< / span > < / code > will
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match either "abc" or "def".
< / p >
< p >
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Parenthesis can be used to group alternations, for example: < code class = "computeroutput" > < span class = "identifier" > ab< / span > < span class = "special" > (< / span > < span class = "identifier" > d< / span > < span class = "special" > |< / span > < span class = "identifier" > ef< / span > < span class = "special" > )< / span > < / code >
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will match either of "abd" or "abef".
< / p >
< p >
Empty alternatives are not allowed (these are almost always a mistake), but
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if you really want an empty alternative use < code class = "computeroutput" > < span class = "special" > (?:)< / span > < / code >
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as a placeholder, for example:
< / p >
< p >
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< code class = "computeroutput" > < span class = "special" > |< / span > < span class = "identifier" > abc< / span > < / code >
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is not a valid expression, but
< / p >
< p >
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< code class = "computeroutput" > < span class = "special" > (?:)|< / span > < span class = "identifier" > abc< / span > < / code >
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is and is equivalent, also the expression:
< / p >
< p >
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< code class = "computeroutput" > < span class = "special" > (?:< / span > < span class = "identifier" > abc< / span > < span class = "special" > )??< / span > < / code > has exactly the same effect.
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< / p >
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< a name = "boost_regex.syntax.perl_syntax.character_sets" > < / a > < h5 >
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< a name = "id499168" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.character_sets" > Character sets< / a >
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< / h5 >
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< p >
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A character set is a bracket-expression starting with < code class = "computeroutput" > < span class = "special" > [< / span > < / code >
and ending with < code class = "computeroutput" > < span class = "special" > ]< / span > < / code > , it defines
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a set of characters, and matches any single character that is a member of
that set.
< / p >
< p >
A bracket expression may contain any combination of the following:
< / p >
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< a name = "boost_regex.syntax.perl_syntax.single_characters" > < / a > < h6 >
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< a name = "id499227" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.single_characters" > Single characters< / a >
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< / h6 >
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< p >
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For example < code class = "computeroutput" > < span class = "special" > [< / span > < span class = "identifier" > abc< / span > < span class = "special" > ]< / span > < / code > , will match any of the characters 'a', 'b',
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or 'c'.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.character_ranges" > < / a > < h6 >
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< a name = "id499277" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.character_ranges" > Character
ranges< / a >
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< / h6 >
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< p >
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For example < code class = "computeroutput" > < span class = "special" > [< / span > < span class = "identifier" > a< / span > < span class = "special" > -< / span > < span class = "identifier" > c< / span > < span class = "special" > ]< / span > < / code >
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will match any single character in the range 'a' to 'c'. By default, for
Perl regular expressions, a character x is within the range y to z, if the
code point of the character lies within the codepoints of the endpoints of
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the range. Alternatively, if you set the < a href = "../ref/syntax_option_type/syntax_option_type_perl.html" title = "Options for Perl Regular Expressions" > < code class = "computeroutput" > < span class = "identifier" > collate< / span > < / code > flag< / a > when constructing the
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regular expression, then ranges are locale sensitive.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.negation" > < / a > < h6 >
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< a name = "id499358" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.negation" > Negation< / a >
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< / h6 >
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< p >
If the bracket-expression begins with the ^ character, then it matches the
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complement of the characters it contains, for example < code class = "computeroutput" > < span class = "special" > [^< / span > < span class = "identifier" > a< / span > < span class = "special" > -< / span > < span class = "identifier" > c< / span > < span class = "special" > ]< / span > < / code > matches any character that is not in the
range < code class = "computeroutput" > < span class = "identifier" > a< / span > < span class = "special" > -< / span > < span class = "identifier" > c< / span > < / code > .
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< / p >
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< a name = "boost_regex.syntax.perl_syntax.character_classes" > < / a > < h6 >
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< a name = "id499440" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.character_classes" > Character
classes< / a >
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< / h6 >
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< p >
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An expression of the form < code class = "computeroutput" > < span class = "special" > [[:< / span > < span class = "identifier" > name< / span > < span class = "special" > :]]< / span > < / code >
matches the named character class "name", for example < code class = "computeroutput" > < span class = "special" > [[:< / span > < span class = "identifier" > lower< / span > < span class = "special" > :]]< / span > < / code > matches any lower case character. See
< a href = "character_classes.html" title = "Character Class Names" > character class names< / a > .
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< / p >
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< a name = "boost_regex.syntax.perl_syntax.collating_elements" > < / a > < h6 >
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< a name = "id499523" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.collating_elements" > Collating
Elements< / a >
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< / h6 >
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< p >
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An expression of the form < code class = "computeroutput" > < span class = "special" > [[.< / span > < span class = "identifier" > col< / span > < span class = "special" > .]< / span > < / code > matches
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the collating element < span class = "emphasis" > < em > col< / em > < / span > . A collating element is any
single character, or any sequence of characters that collates as a single
unit. Collating elements may also be used as the end point of a range, for
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example: < code class = "computeroutput" > < span class = "special" > [[.< / span > < span class = "identifier" > ae< / span > < span class = "special" > .]-< / span > < span class = "identifier" > c< / span > < span class = "special" > ]< / span > < / code >
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matches the character sequence "ae", plus any single character
in the range "ae"-c, assuming that "ae" is treated as
a single collating element in the current locale.
< / p >
< p >
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As an extension, a collating element may also be specified via it's < a href = "collating_names.html" title = "Collating Names" > symbolic name< / a > , for example:
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< / p >
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< pre class = "programlisting" > < span class = "special" > [[.< / span > < span class = "identifier" > NUL< / span > < span class = "special" > .]]< / span >
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< / pre >
< p >
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matches a < code class = "computeroutput" > < span class = "special" > \< / span > < span class = "number" > 0< / span > < / code >
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character.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.equivalence_classes" > < / a > < h6 >
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< a name = "id499675" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.equivalence_classes" > Equivalence
classes< / a >
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< / h6 >
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< p >
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An expression of the form < code class = "computeroutput" > < span class = "special" > [[=< / span > < span class = "identifier" > col< / span > < span class = "special" > =]]< / span > < / code > ,
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matches any character or collating element whose primary sort key is the
same as that for collating element < span class = "emphasis" > < em > col< / em > < / span > , as with collating
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elements the name < span class = "emphasis" > < em > col< / em > < / span > may be a < a href = "collating_names.html" title = "Collating Names" > symbolic
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name< / a > . A primary sort key is one that ignores case, accentation, or
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locale-specific tailorings; so for example < code class = "computeroutput" > < span class = "special" > [[=< / span > < span class = "identifier" > a< / span > < span class = "special" > =]]< / span > < / code > matches
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any of the characters: a, <20> , <20> , <20> , <20> , <20> , <20> , A, <20> , <20> , <20> , <20> , <20> and <20> . Unfortunately implementation
of this is reliant on the platform's collation and localisation support;
this feature can not be relied upon to work portably across all platforms,
or even all locales on one platform.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.escaped_characters" > < / a > < h6 >
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< a name = "id499778" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.escaped_characters" > Escaped
Characters< / a >
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< / h6 >
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< p >
All the escape sequences that match a single character, or a single character
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class are permitted within a character class definition. For example < code class = "computeroutput" > < span class = "special" > [\[\]]< / span > < / code > would match either of < code class = "computeroutput" > < span class = "special" > [< / span > < / code > or < code class = "computeroutput" > < span class = "special" > ]< / span > < / code >
while < code class = "computeroutput" > < span class = "special" > [\< / span > < span class = "identifier" > W< / span > < span class = "special" > \< / span > < span class = "identifier" > d< / span > < span class = "special" > ]< / span > < / code >
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would match any character that is either a "digit", < span class = "emphasis" > < em > or< / em > < / span >
is < span class = "emphasis" > < em > not< / em > < / span > a "word" character.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.combinations" > < / a > < h6 >
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< a name = "id499884" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.combinations" > Combinations< / a >
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< / h6 >
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< p >
All of the above can be combined in one character set declaration, for example:
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< code class = "computeroutput" > < span class = "special" > [[:< / span > < span class = "identifier" > digit< / span > < span class = "special" > :]< / span > < span class = "identifier" > a< / span > < span class = "special" > -< / span > < span class = "identifier" > c< / span > < span class = "special" > [.< / span > < span class = "identifier" > NUL< / span > < span class = "special" > .]]< / span > < / code > .
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< / p >
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< a name = "boost_regex.syntax.perl_syntax.escapes" > < / a > < h5 >
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< a name = "id499962" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.escapes" > Escapes< / a >
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< / h5 >
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< p >
Any special character preceded by an escape shall match itself.
< / p >
< p >
The following escape sequences are all synonyms for single characters:
< / p >
< div class = "informaltable" > < table class = "table" >
< colgroup >
< col >
< col >
< / colgroup >
< thead > < tr >
< th >
< p >
Escape
< / p >
< / th >
< th >
< p >
Character
< / p >
< / th >
< / tr > < / thead >
< tbody >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > a< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > a< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > e< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "number" > 0x1B< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > f< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > f< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > n< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > n< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > r< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > r< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > t< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > t< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > v< / span >
< / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > v< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > b< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > b< / span > < / code >
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(but only inside a character class declaration).
< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > cX< / span > < / code >
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< / p >
< / td >
< td >
< p >
An ASCII escape sequence - the character whose code point is X %
32
< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > xdd< / span > < / code >
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< / p >
< / td >
< td >
< p >
A hexadecimal escape sequence - matches the single character whose
code point is 0xdd.
< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > x< / span > < span class = "special" > {< / span > < span class = "identifier" > dddd< / span > < span class = "special" > }< / span > < / code >
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< / p >
< / td >
< td >
< p >
A hexadecimal escape sequence - matches the single character whose
code point is 0xdddd.
< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "number" > 0ddd< / span > < / code >
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< / p >
< / td >
< td >
< p >
An octal escape sequence - matches the single character whose code
point is 0ddd.
< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > N< / span > < span class = "special" > {< / span > < span class = "identifier" > name< / span > < span class = "special" > }< / span > < / code >
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< / p >
< / td >
< td >
< p >
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Matches the single character which has the < a href = "collating_names.html" title = "Collating Names" > symbolic
name< / a > < span class = "emphasis" > < em > name< / em > < / span > . For example < code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > N< / span > < span class = "special" > {< / span > < span class = "identifier" > newline< / span > < span class = "special" > }< / span > < / code > matches the single character \n.
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< / p >
< / td >
< / tr >
< / tbody >
< / table > < / div >
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< a name = "boost_regex.syntax.perl_syntax._quot_single_character_quot__character_classes_" > < / a > < h6 >
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< a name = "id500675" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax._quot_single_character_quot__character_classes_" > "Single
character" character classes:< / a >
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< / h6 >
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< p >
Any escaped character < span class = "emphasis" > < em > x< / em > < / span > , if < span class = "emphasis" > < em > x< / em > < / span > is
the name of a character class shall match any character that is a member
of that class, and any escaped character < span class = "emphasis" > < em > X< / em > < / span > , if < span class = "emphasis" > < em > x< / em > < / span >
is the name of a character class, shall match any character not in that class.
< / p >
< p >
The following are supported by default:
< / p >
< div class = "informaltable" > < table class = "table" >
< colgroup >
< col >
< col >
< / colgroup >
< thead > < tr >
< th >
< p >
Escape sequence
< / p >
< / th >
< th >
< p >
Equivalent to
< / p >
< / th >
< / tr > < / thead >
< tbody >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > d< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > [[:< / span > < span class = "identifier" > digit< / span > < span class = "special" > :]]< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > l< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > [[:< / span > < span class = "identifier" > lower< / span > < span class = "special" > :]]< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > s< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > [[:< / span > < span class = "identifier" > space< / span > < span class = "special" > :]]< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > u< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > [[:< / span > < span class = "identifier" > upper< / span > < span class = "special" > :]]< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > w< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > [[:< / span > < span class = "identifier" > word< / span > < span class = "special" > :]]< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > D< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > [^[:< / span > < span class = "identifier" > digit< / span > < span class = "special" > :]]< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > L< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > [^[:< / span > < span class = "identifier" > lower< / span > < span class = "special" > :]]< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > S< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > [^[:< / span > < span class = "identifier" > space< / span > < span class = "special" > :]]< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > U< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > [^[:< / span > < span class = "identifier" > upper< / span > < span class = "special" > :]]< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > W< / span > < / code >
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< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > [^[:< / span > < span class = "identifier" > word< / span > < span class = "special" > :]]< / span > < / code >
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< / p >
< / td >
< / tr >
< / tbody >
< / table > < / div >
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< a name = "boost_regex.syntax.perl_syntax.character_properties" > < / a > < h6 >
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< a name = "id501307" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.character_properties" > Character
Properties< / a >
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< / h6 >
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< p >
The character property names in the following table are all equivalent to
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the < a href = "character_classes.html" title = "Character Class Names" > names used in character
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classes< / a > .
< / p >
< div class = "informaltable" > < table class = "table" >
< colgroup >
< col >
< col >
< col >
< / colgroup >
< thead > < tr >
< th >
< p >
Form
< / p >
< / th >
< th >
< p >
Description
< / p >
< / th >
< th >
< p >
Equivalent character set form
< / p >
< / th >
< / tr > < / thead >
< tbody >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > pX< / span > < / code >
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< / p >
< / td >
< td >
< p >
Matches any character that has the property X.
< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > [[:< / span > < span class = "identifier" > X< / span > < span class = "special" > :]]< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > p< / span > < span class = "special" > {< / span > < span class = "identifier" > Name< / span > < span class = "special" > }< / span > < / code >
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< / p >
< / td >
< td >
< p >
Matches any character that has the property Name.
< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > [[:< / span > < span class = "identifier" > Name< / span > < span class = "special" > :]]< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > PX< / span > < / code >
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< / p >
< / td >
< td >
< p >
Matches any character that does not have the property X.
< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > [^[:< / span > < span class = "identifier" > X< / span > < span class = "special" > :]]< / span > < / code >
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< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > P< / span > < span class = "special" > {< / span > < span class = "identifier" > Name< / span > < span class = "special" > }< / span > < / code >
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< / p >
< / td >
< td >
< p >
Matches any character that does not have the property Name.
< / p >
< / td >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > [^[:< / span > < span class = "identifier" > Name< / span > < span class = "special" > :]]< / span > < / code >
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< / p >
< / td >
< / tr >
< / tbody >
< / table > < / div >
< p >
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For example < code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > pd< / span > < / code >
matches any "digit" character, as does < code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > p< / span > < span class = "special" > {< / span > < span class = "identifier" > digit< / span > < span class = "special" > }< / span > < / code > .
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< / p >
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< a name = "boost_regex.syntax.perl_syntax.word_boundaries" > < / a > < h6 >
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< a name = "id501717" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.word_boundaries" > Word Boundaries< / a >
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< / h6 >
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< p >
The following escape sequences match the boundaries of words:
< / p >
< p >
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< code class = "computeroutput" > < span class = "special" > \< < / span > < / code > Matches the start of a
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word.
< / p >
< p >
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< code class = "computeroutput" > < span class = "special" > \> < / span > < / code > Matches the end of a word.
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< / p >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > b< / span > < / code >
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Matches a word boundary (the start or end of a word).
< / p >
< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > B< / span > < / code >
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Matches only when not at a word boundary.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.buffer_boundaries" > < / a > < h6 >
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< a name = "id501818" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.buffer_boundaries" > Buffer boundaries< / a >
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< / h6 >
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< p >
The following match only at buffer boundaries: a "buffer" in this
context is the whole of the input text that is being matched against (note
that ^ and $ may match embedded newlines within the text).
< / p >
< p >
\` Matches at the start of a buffer only.
< / p >
< p >
\' Matches at the end of a buffer only.
< / p >
< p >
\A Matches at the start of a buffer only (the same as \`).
< / p >
< p >
\z Matches at the end of a buffer only (the same as \').
< / p >
< p >
\Z Matches an optional sequence of newlines at the end of a buffer: equivalent
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to the regular expression < code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > n< / span > < span class = "special" > *\< / span > < span class = "identifier" > z< / span > < / code >
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< / p >
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< a name = "boost_regex.syntax.perl_syntax.continuation_escape" > < / a > < h6 >
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< a name = "id501902" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.continuation_escape" > Continuation
Escape< / a >
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< / h6 >
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< p >
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The sequence < code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > G< / span > < / code >
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matches only at the end of the last match found, or at the start of the text
being matched if no previous match was found. This escape useful if you're
iterating over the matches contained within a text, and you want each subsequence
match to start where the last one ended.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.quoting_escape" > < / a > < h6 >
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< a name = "id501952" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.quoting_escape" > Quoting escape< / a >
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< / h6 >
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< p >
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The escape sequence < code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > Q< / span > < / code >
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begins a "quoted sequence": all the subsequent characters are treated
as literals, until either the end of the regular expression or \E is found.
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For example the expression: < code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > Q< / span > < span class = "special" > \*+\< / span > < span class = "identifier" > Ea< / span > < span class = "special" > +< / span > < / code > would match either of:
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< / p >
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< pre class = "programlisting" > < span class = "special" > \*+< / span > < span class = "identifier" > a< / span >
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< span class = "special" > \*+< / span > < span class = "identifier" > aaa< / span >
< / pre >
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< a name = "boost_regex.syntax.perl_syntax.unicode_escapes" > < / a > < h6 >
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< a name = "id502058" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.unicode_escapes" > Unicode escapes< / a >
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< / h6 >
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< p >
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< code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > C< / span > < / code >
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Matches a single code point: in Boost regex this has exactly the same effect
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as a "." operator. < code class = "computeroutput" > < span class = "special" > \< / span > < span class = "identifier" > X< / span > < / code > Matches a combining character sequence:
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that is any non-combining character followed by a sequence of zero or more
combining characters.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.any_other_escape" > < / a > < h6 >
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< a name = "id502122" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.any_other_escape" > Any other
escape< / a >
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< / h6 >
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< p >
Any other escape sequence matches the character that is escaped, for example
\@ matches a literal '@'.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.perl_extended_patterns" > < / a > < h5 >
2008-02-21 12:58:15 +00:00
< a name = "id502151" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.perl_extended_patterns" > Perl
Extended Patterns< / a >
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< / h5 >
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< p >
Perl-specific extensions to the regular expression syntax all start with
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< code class = "computeroutput" > < span class = "special" > (?< / span > < / code > .
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< / p >
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< a name = "boost_regex.syntax.perl_syntax.comments" > < / a > < h6 >
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< a name = "id502192" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.comments" > Comments< / a >
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< / h6 >
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< p >
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< code class = "computeroutput" > < span class = "special" > (?< / span > # < span class = "special" > ...< / span >
< span class = "special" > )< / span > < / code > is treated as a comment, it's contents
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are ignored.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.modifiers" > < / a > < h6 >
2008-02-21 12:58:15 +00:00
< a name = "id502245" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.modifiers" > Modifiers< / a >
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< / h6 >
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< p >
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< code class = "computeroutput" > < span class = "special" > (?< / span > < span class = "identifier" > imsx< / span > < span class = "special" > -< / span > < span class = "identifier" > imsx< / span > < span class = "special" > ...< / span > < span class = "special" > )< / span > < / code > alters
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which of the perl modifiers are in effect within the pattern, changes take
effect from the point that the block is first seen and extend to any enclosing
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< code class = "computeroutput" > < span class = "special" > )< / span > < / code > . Letters before a '-' turn
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that perl modifier on, letters afterward, turn it off.
< / p >
< p >
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< code class = "computeroutput" > < span class = "special" > (?< / span > < span class = "identifier" > imsx< / span > < span class = "special" > -< / span > < span class = "identifier" > imsx< / span > < span class = "special" > :< / span > < span class = "identifier" > pattern< / span > < span class = "special" > )< / span > < / code >
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applies the specified modifiers to pattern only.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.non_marking_groups" > < / a > < h6 >
2008-02-21 12:58:15 +00:00
< a name = "id502372" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.non_marking_groups" > Non-marking
groups< / a >
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< / h6 >
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< p >
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< code class = "computeroutput" > < span class = "special" > (?:< / span > < span class = "identifier" > pattern< / span > < span class = "special" > )< / span > < / code > lexically groups pattern, without generating
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an additional sub-expression.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.lookahead" > < / a > < h6 >
2008-02-21 12:58:15 +00:00
< a name = "id502423" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.lookahead" > Lookahead< / a >
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< / h6 >
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< p >
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< code class = "computeroutput" > < span class = "special" > (?=< / span > < span class = "identifier" > pattern< / span > < span class = "special" > )< / span > < / code > consumes zero characters, only if pattern
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matches.
< / p >
< p >
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< code class = "computeroutput" > < span class = "special" > (?!< / span > < span class = "identifier" > pattern< / span > < span class = "special" > )< / span > < / code > consumes zero characters, only if pattern
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does not match.
< / p >
< p >
Lookahead is typically used to create the logical AND of two regular expressions,
for example if a password must contain a lower case letter, an upper case
letter, a punctuation symbol, and be at least 6 characters long, then the
expression:
< / p >
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< pre class = "programlisting" > < span class = "special" > (?=.*[[:< / span > < span class = "identifier" > lower< / span > < span class = "special" > :]])(?=.*[[:< / span > < span class = "identifier" > upper< / span > < span class = "special" > :]])(?=.*[[:< / span > < span class = "identifier" > punct< / span > < span class = "special" > :]]).{< / span > < span class = "number" > 6< / span > < span class = "special" > ,}< / span >
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< / pre >
< p >
could be used to validate the password.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.lookbehind" > < / a > < h6 >
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< a name = "id502564" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.lookbehind" > Lookbehind< / a >
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< / h6 >
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< p >
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< code class = "computeroutput" > < span class = "special" > (?< =< / span > < span class = "identifier" > pattern< / span > < span class = "special" > )< / span > < / code > consumes zero characters, only if pattern
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could be matched against the characters preceding the current position (pattern
must be of fixed length).
< / p >
< p >
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< code class = "computeroutput" > < span class = "special" > (?< !< / span > < span class = "identifier" > pattern< / span > < span class = "special" > )< / span > < / code > consumes zero characters, only if pattern
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could not be matched against the characters preceding the current position
(pattern must be of fixed length).
< / p >
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< a name = "boost_regex.syntax.perl_syntax.independent_sub_expressions" > < / a > < h6 >
2008-02-21 12:58:15 +00:00
< a name = "id502643" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.independent_sub_expressions" > Independent
sub-expressions< / a >
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< / h6 >
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< p >
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< code class = "computeroutput" > < span class = "special" > (?> < / span > < span class = "identifier" > pattern< / span > < span class = "special" > )< / span > < / code > < span class = "emphasis" > < em > pattern< / em > < / span > is matched
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independently of the surrounding patterns, the expression will never backtrack
into < span class = "emphasis" > < em > pattern< / em > < / span > . Independent sub-expressions are typically
used to improve performance; only the best possible match for pattern will
be considered, if this doesn't allow the expression as a whole to match then
no match is found at all.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.conditional_expressions" > < / a > < h6 >
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< a name = "id502707" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.conditional_expressions" > Conditional
Expressions< / a >
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< / h6 >
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< p >
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< code class = "computeroutput" > < span class = "special" > (?(< / span > < span class = "identifier" > condition< / span > < span class = "special" > )< / span > < span class = "identifier" > yes< / span > < span class = "special" > -< / span > < span class = "identifier" > pattern< / span > < span class = "special" > |< / span > < span class = "identifier" > no< / span > < span class = "special" > -< / span > < span class = "identifier" > pattern< / span > < span class = "special" > )< / span > < / code > attempts to match < span class = "emphasis" > < em > yes-pattern< / em > < / span >
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if the < span class = "emphasis" > < em > condition< / em > < / span > is true, otherwise attempts to match
< span class = "emphasis" > < em > no-pattern< / em > < / span > .
< / p >
< p >
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< code class = "computeroutput" > < span class = "special" > (?(< / span > < span class = "identifier" > condition< / span > < span class = "special" > )< / span > < span class = "identifier" > yes< / span > < span class = "special" > -< / span > < span class = "identifier" > pattern< / span > < span class = "special" > )< / span > < / code >
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attempts to match < span class = "emphasis" > < em > yes-pattern< / em > < / span > if the < span class = "emphasis" > < em > condition< / em > < / span >
is true, otherwise fails.
< / p >
< p >
< span class = "emphasis" > < em > condition< / em > < / span > may be either a forward lookahead assert,
or the index of a marked sub-expression (the condition becomes true if the
sub-expression has been matched).
< / p >
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< a name = "boost_regex.syntax.perl_syntax.operator_precedence" > < / a > < h5 >
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< a name = "id502875" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.operator_precedence" > Operator
precedence< / a >
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< / h5 >
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< p >
The order of precedence for of operators is as follows:
< / p >
< div class = "orderedlist" > < ol type = "1" >
< li >
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Collation-related bracket symbols < code class = "computeroutput" > < span class = "special" > [==]< / span >
< span class = "special" > [::]< / span > < span class = "special" > [..]< / span > < / code >
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< / li >
< li >
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Escaped characters < code class = "computeroutput" > < span class = "special" > \< / span > < / code >
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< / li >
< li >
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Character set (bracket expression) < code class = "computeroutput" > < span class = "special" > []< / span > < / code >
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< / li >
< li >
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Grouping < code class = "computeroutput" > < span class = "special" > ()< / span > < / code >
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< / li >
< li >
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Single-character-ERE duplication < code class = "computeroutput" > < span class = "special" > *< / span >
< span class = "special" > +< / span > < span class = "special" > ?< / span > < span class = "special" > {< / span > < span class = "identifier" > m< / span > < span class = "special" > ,< / span > < span class = "identifier" > n< / span > < span class = "special" > }< / span > < / code >
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< / li >
< li >
Concatenation
< / li >
< li >
Anchoring ^$
< / li >
< li >
Alternation |
< / li >
< / ol > < / div >
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< a name = "boost_regex.syntax.perl_syntax.what_gets_matched" > < / a > < h4 >
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< a name = "id503053" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.what_gets_matched" > What gets
matched< / a >
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< / h4 >
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< p >
If you view the regular expression as a directed (possibly cyclic) graph,
then the best match found is the first match found by a depth-first-search
performed on that graph, while matching the input text.
< / p >
< p >
Alternatively:
< / p >
< p >
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The best match found is the < a href = "leftmost_longest_rule.html" title = "The Leftmost Longest Rule" > leftmost
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match< / a > , with individual elements matched as follows;
< / p >
< div class = "informaltable" > < table class = "table" >
< colgroup >
< col >
< col >
< / colgroup >
< thead > < tr >
< th >
< p >
Construct
< / p >
< / th >
< th >
< p >
What gets matched
< / p >
< / th >
< / tr > < / thead >
< tbody >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "identifier" > AtomA< / span > < span class = "identifier" > AtomB< / span > < / code >
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< / p >
< / td >
< td >
< p >
Locates the best match for < span class = "emphasis" > < em > AtomA< / em > < / span > that has a
following match for < span class = "emphasis" > < em > AtomB< / em > < / span > .
< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "identifier" > Expression1< / span > < span class = "special" > |< / span >
< span class = "identifier" > Expression2< / span > < / code >
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< / p >
< / td >
< td >
< p >
If < span class = "emphasis" > < em > Expresion1< / em > < / span > can be matched then returns that
match, otherwise attempts to match < span class = "emphasis" > < em > Expression2< / em > < / span > .
< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "identifier" > S< / span > < span class = "special" > {< / span > < span class = "identifier" > N< / span > < span class = "special" > }< / span > < / code >
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< / p >
< / td >
< td >
< p >
Matches < span class = "emphasis" > < em > S< / em > < / span > repeated exactly N times.
< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "identifier" > S< / span > < span class = "special" > {< / span > < span class = "identifier" > N< / span > < span class = "special" > ,< / span > < span class = "identifier" > M< / span > < span class = "special" > }< / span > < / code >
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< / p >
< / td >
< td >
< p >
Matches S repeated between N and M times, and as many times as possible.
< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "identifier" > S< / span > < span class = "special" > {< / span > < span class = "identifier" > N< / span > < span class = "special" > ,< / span > < span class = "identifier" > M< / span > < span class = "special" > }?< / span > < / code >
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< / p >
< / td >
< td >
< p >
Matches S repeated between N and M times, and as few times as possible.
< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "identifier" > S< / span > < span class = "special" > ?,< / span >
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< span class = "identifier" > S< / span > < span class = "special" > *,< / span >
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< span class = "identifier" > S< / span > < span class = "special" > +< / span > < / code >
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< / p >
< / td >
< td >
< p >
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The same as < code class = "computeroutput" > < span class = "identifier" > S< / span > < span class = "special" > {< / span > < span class = "number" > 0< / span > < span class = "special" > ,< / span > < span class = "number" > 1< / span > < span class = "special" > }< / span > < / code > ,
< code class = "computeroutput" > < span class = "identifier" > S< / span > < span class = "special" > {< / span > < span class = "number" > 0< / span > < span class = "special" > ,< / span > < span class = "identifier" > UINT_MAX< / span > < span class = "special" > }< / span > < / code > ,
< code class = "computeroutput" > < span class = "identifier" > S< / span > < span class = "special" > {< / span > < span class = "number" > 1< / span > < span class = "special" > ,< / span > < span class = "identifier" > UINT_MAX< / span > < span class = "special" > }< / span > < / code >
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respectively.
< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "identifier" > S< / span > < span class = "special" > ??,< / span >
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< span class = "identifier" > S< / span > < span class = "special" > *?,< / span >
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< span class = "identifier" > S< / span > < span class = "special" > +?< / span > < / code >
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< / p >
< / td >
< td >
< p >
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The same as < code class = "computeroutput" > < span class = "identifier" > S< / span > < span class = "special" > {< / span > < span class = "number" > 0< / span > < span class = "special" > ,< / span > < span class = "number" > 1< / span > < span class = "special" > }?< / span > < / code > ,
< code class = "computeroutput" > < span class = "identifier" > S< / span > < span class = "special" > {< / span > < span class = "number" > 0< / span > < span class = "special" > ,< / span > < span class = "identifier" > UINT_MAX< / span > < span class = "special" > }?< / span > < / code > ,
< code class = "computeroutput" > < span class = "identifier" > S< / span > < span class = "special" > {< / span > < span class = "number" > 1< / span > < span class = "special" > ,< / span > < span class = "identifier" > UINT_MAX< / span > < span class = "special" > }?< / span > < / code >
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respectively.
< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > (?> < / span > < span class = "identifier" > S< / span > < span class = "special" > )< / span > < / code >
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< / p >
< / td >
< td >
< p >
Matches the best match for < span class = "emphasis" > < em > S< / em > < / span > , and only that.
< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > (?=< / span > < span class = "identifier" > S< / span > < span class = "special" > ),< / span > < span class = "special" > (?< =< / span > < span class = "identifier" > S< / span > < span class = "special" > )< / span > < / code >
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< / p >
< / td >
< td >
< p >
Matches only the best match for < span class = "emphasis" > < em > S< / em > < / span > (this is only
visible if there are capturing parenthesis within < span class = "emphasis" > < em > S< / em > < / span > ).
< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > (?!< / span > < span class = "identifier" > S< / span > < span class = "special" > ),< / span > < span class = "special" > (?< !< / span > < span class = "identifier" > S< / span > < span class = "special" > )< / span > < / code >
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< / p >
< / td >
< td >
< p >
Considers only whether a match for S exists or not.
< / p >
< / td >
< / tr >
< tr >
< td >
< p >
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< code class = "computeroutput" > < span class = "special" > (?(< / span > < span class = "identifier" > condition< / span > < span class = "special" > )< / span > < span class = "identifier" > yes< / span > < span class = "special" > -< / span > < span class = "identifier" > pattern< / span >
< span class = "special" > |< / span > < span class = "identifier" > no< / span > < span class = "special" > -< / span > < span class = "identifier" > pattern< / span > < span class = "special" > )< / span > < / code >
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< / p >
< / td >
< td >
< p >
If condition is true, then only yes-pattern is considered, otherwise
only no-pattern is considered.
< / p >
< / td >
< / tr >
< / tbody >
< / table > < / div >
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< a name = "boost_regex.syntax.perl_syntax.variations" > < / a > < h4 >
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< a name = "id503968" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.variations" > Variations< / a >
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< / h4 >
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< p >
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The < a href = "../ref/syntax_option_type/syntax_option_type_perl.html" title = "Options for Perl Regular Expressions" > options
< code class = "computeroutput" > < span class = "identifier" > normal< / span > < / code > , < code class = "computeroutput" > < span class = "identifier" > ECMAScript< / span > < / code > ,
< code class = "computeroutput" > < span class = "identifier" > JavaScript< / span > < / code > and < code class = "computeroutput" > < span class = "identifier" > JScript< / span > < / code > < / a > are all synonyms for < code class = "computeroutput" > < span class = "identifier" > perl< / span > < / code > .
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< / p >
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< a name = "boost_regex.syntax.perl_syntax.options" > < / a > < h4 >
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< a name = "id504063" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.options" > Options< / a >
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< / h4 >
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< p >
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There are a < a href = "../ref/syntax_option_type/syntax_option_type_perl.html" title = "Options for Perl Regular Expressions" > variety
of flags< / a > that may be combined with the < code class = "computeroutput" > < span class = "identifier" > perl< / span > < / code >
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option when constructing the regular expression, in particular note that
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the < code class = "computeroutput" > < span class = "identifier" > newline_alt< / span > < / code > option alters
the syntax, while the < code class = "computeroutput" > < span class = "identifier" > collate< / span > < / code > ,
< code class = "computeroutput" > < span class = "identifier" > nosubs< / span > < / code > and < code class = "computeroutput" > < span class = "identifier" > icase< / span > < / code > options modify how the case and locale
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sensitivity are to be applied.
< / p >
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< a name = "boost_regex.syntax.perl_syntax.pattern_modifiers" > < / a > < h4 >
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< a name = "id504164" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.pattern_modifiers" > Pattern
Modifiers< / a >
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< / h4 >
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< p >
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The perl < code class = "computeroutput" > < span class = "identifier" > smix< / span > < / code > modifiers can
either be applied using a < code class = "computeroutput" > < span class = "special" > (?< / span > < span class = "identifier" > smix< / span > < span class = "special" > -< / span > < span class = "identifier" > smix< / span > < span class = "special" > )< / span > < / code > prefix to the regular expression, or with
one of the < a href = "../ref/syntax_option_type/syntax_option_type_perl.html" title = "Options for Perl Regular Expressions" > regex-compile
time flags < code class = "computeroutput" > < span class = "identifier" > no_mod_m< / span > < / code > , < code class = "computeroutput" > < span class = "identifier" > mod_x< / span > < / code > , < code class = "computeroutput" > < span class = "identifier" > mod_s< / span > < / code > ,
and < code class = "computeroutput" > < span class = "identifier" > no_mod_s< / span > < / code > < / a > .
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< / p >
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< a name = "boost_regex.syntax.perl_syntax.references" > < / a > < h4 >
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< a name = "id504291" > < / a >
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< a href = "perl_syntax.html#boost_regex.syntax.perl_syntax.references" > References< / a >
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< / h4 >
2007-06-08 09:23:23 +00:00
< p >
< a href = "http://perldoc.perl.org/perlre.html" target = "_top" > Perl 5.8< / a > .
< / p >
< / div >
< table xmlns:rev = "http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width = "100%" > < tr >
< td align = "left" > < / td >
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< td align = "right" > < div class = "copyright-footer" > Copyright <20> 1998 -2007 John Maddock< p >
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Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at < a href = "http://www.boost.org/LICENSE_1_0.txt" target = "_top" > http://www.boost.org/LICENSE_1_0.txt< / a > )
2007-12-14 10:11:21 +00:00
< / p >
< / div > < / td >
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< / tr > < / table >
< hr >
< div class = "spirit-nav" >
< a accesskey = "p" href = "../syntax.html" > < img src = "../../../../../../doc/html/images/prev.png" alt = "Prev" > < / a > < a accesskey = "u" href = "../syntax.html" > < img src = "../../../../../../doc/html/images/up.png" alt = "Up" > < / a > < a accesskey = "h" href = "../../index.html" > < img src = "../../../../../../doc/html/images/home.png" alt = "Home" > < / a > < a accesskey = "n" href = "basic_extended.html" > < img src = "../../../../../../doc/html/images/next.png" alt = "Next" > < / a >
< / div >
< / body >
< / html >
