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<title>POSIX Extended Regular Expression Syntax</title>
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="boost_regex.syntax.basic_extended"></a><a class="link" href="basic_extended.html" title="POSIX Extended Regular Expression Syntax">POSIX Extended Regular
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Expression Syntax</a>
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</h3></div></div></div>
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<h4>
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<a name="boost_regex.syntax.basic_extended.h0"></a>
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<span class="phrase"><a name="boost_regex.syntax.basic_extended.synopsis"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.synopsis">Synopsis</a>
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</h4>
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<p>
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The POSIX-Extended regular expression syntax is supported by the POSIX C
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regular expression API's, and variations are used by the utilities <code class="computeroutput"><span class="identifier">egrep</span></code> and <code class="computeroutput"><span class="identifier">awk</span></code>.
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You can construct POSIX extended regular expressions in Boost.Regex by passing
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the flag <code class="computeroutput"><span class="identifier">extended</span></code> to the
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regex constructor, for example:
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</p>
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<pre class="programlisting"><span class="comment">// e1 is a case sensitive POSIX-Extended expression:</span>
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<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="identifier">boost</span><span class="special">::</span><span class="identifier">regex</span><span class="special">::</span><span class="identifier">extended</span><span class="special">);</span>
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<span class="comment">// e2 a case insensitive POSIX-Extended expression:</span>
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<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">extended</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>
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</pre>
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<a name="boost_regex.posix_extended_syntax"></a><h4>
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<a name="boost_regex.syntax.basic_extended.h1"></a>
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<span class="phrase"><a name="boost_regex.syntax.basic_extended.posix_extended_syntax"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.posix_extended_syntax">POSIX Extended
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Syntax</a>
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</h4>
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<p>
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In POSIX-Extended regular expressions, all characters match themselves except
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for the following special characters:
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</p>
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<pre class="programlisting">.[{}()\*+?|^$</pre>
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<h5>
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<a name="boost_regex.syntax.basic_extended.h2"></a>
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<span class="phrase"><a name="boost_regex.syntax.basic_extended.wildcard"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.wildcard">Wildcard:</a>
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</h5>
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<p>
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The single character '.' when used outside of a character set will match
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any single character except:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
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<li class="listitem">
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The NULL character when the flag <code class="computeroutput"><span class="identifier">match_no_dot_null</span></code>
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is passed to the matching algorithms.
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</li>
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<li class="listitem">
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The newline character when the flag <code class="computeroutput"><span class="identifier">match_not_dot_newline</span></code>
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is passed to the matching algorithms.
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</li>
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</ul></div>
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<h5>
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<a name="boost_regex.syntax.basic_extended.h3"></a>
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<span class="phrase"><a name="boost_regex.syntax.basic_extended.anchors"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.anchors">Anchors:</a>
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</h5>
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<p>
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A '^' character shall match the start of a line when used as the first character
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of an expression, or the first character of a sub-expression.
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</p>
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<p>
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A '$' character shall match the end of a line when used as the last character
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of an expression, or the last character of a sub-expression.
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</p>
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<h5>
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<a name="boost_regex.syntax.basic_extended.h4"></a>
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<span class="phrase"><a name="boost_regex.syntax.basic_extended.marked_sub_expressions"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.marked_sub_expressions">Marked
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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
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<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
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matching algorithms. Marked sub-expressions can also repeated, or referred
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to by a back-reference.
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</p>
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<h5>
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<a name="boost_regex.syntax.basic_extended.h5"></a>
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<span class="phrase"><a name="boost_regex.syntax.basic_extended.repeats"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.repeats">Repeats:</a>
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</h5>
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<p>
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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>,
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<code class="computeroutput"><span class="special">+</span></code>, <code class="computeroutput"><span class="special">?</span></code>,
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and <code class="computeroutput"><span class="special">{}</span></code> operators.
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</p>
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<p>
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The <code class="computeroutput"><span class="special">*</span></code> operator will match the
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preceding atom <span class="emphasis"><em>zero or more times</em></span>, for example the expression
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<code class="computeroutput"><span class="identifier">a</span><span class="special">*</span><span class="identifier">b</span></code> will match any of the following:
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</p>
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<pre class="programlisting">b
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ab
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aaaaaaaab
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</pre>
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<p>
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The <code class="computeroutput"><span class="special">+</span></code> operator will match the
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preceding atom <span class="emphasis"><em>one or more times</em></span>, for example the expression
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a+b will match any of the following:
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</p>
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<pre class="programlisting">ab
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aaaaaaaab
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</pre>
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<p>
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But will not match:
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</p>
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<pre class="programlisting">b
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</pre>
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<p>
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The <code class="computeroutput"><span class="special">?</span></code> operator will match the
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preceding atom <span class="emphasis"><em>zero or one times</em></span>, for example the expression
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<code class="computeroutput"><span class="identifier">ca</span><span class="special">?</span><span class="identifier">b</span></code> will match any of the following:
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</p>
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<pre class="programlisting">cb
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cab
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</pre>
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<p>
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But will not match:
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</p>
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<pre class="programlisting">caab
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</pre>
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<p>
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An atom can also be repeated with a bounded repeat:
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</p>
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<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 <span class="emphasis"><em>exactly n times</em></span>.
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</p>
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<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 <span class="emphasis"><em>n or more times</em></span>.
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</p>
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<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 <span class="emphasis"><em>between n
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and m times inclusive</em></span>.
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</p>
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<p>
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For example:
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</p>
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<pre class="programlisting">^a{2,3}$</pre>
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<p>
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Will match either of:
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</p>
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<pre class="programlisting"><span class="identifier">aa</span>
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<span class="identifier">aaa</span>
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</pre>
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<p>
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But neither of:
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</p>
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<pre class="programlisting"><span class="identifier">a</span>
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<span class="identifier">aaaa</span>
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</pre>
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<p>
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It is an error to use a repeat operator, if the preceding construct can not
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be repeated, for example:
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</p>
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<pre class="programlisting"><span class="identifier">a</span><span class="special">(*)</span>
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</pre>
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<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.
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</p>
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<h5>
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<a name="boost_regex.syntax.basic_extended.h6"></a>
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<span class="phrase"><a name="boost_regex.syntax.basic_extended.back_references"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.back_references">Back
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references:</a>
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</h5>
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<p>
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An escape character followed by a digit <span class="emphasis"><em>n</em></span>, where <span class="emphasis"><em>n</em></span>
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is in the range 1-9, matches the same string that was matched by sub-expression
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<span class="emphasis"><em>n</em></span>. For example the expression:
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</p>
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<pre class="programlisting">^(a*)[^a]*\1$</pre>
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<p>
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Will match the string:
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</p>
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<pre class="programlisting"><span class="identifier">aaabbaaa</span>
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</pre>
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<p>
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But not the string:
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</p>
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<pre class="programlisting"><span class="identifier">aaabba</span>
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</pre>
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<div class="caution"><table border="0" summary="Caution">
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<tr>
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<td rowspan="2" align="center" valign="top" width="25"><img alt="[Caution]" src="../../../../../../doc/src/images/caution.png"></td>
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<th align="left">Caution</th>
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</tr>
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<tr><td align="left" valign="top"><p>
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The POSIX standard does not support back-references for "extended"
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regular expressions, this is a compatible extension to that standard.
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</p></td></tr>
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</table></div>
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<h5>
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<a name="boost_regex.syntax.basic_extended.h7"></a>
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<span class="phrase"><a name="boost_regex.syntax.basic_extended.alternation"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.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
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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".
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</p>
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<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".
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</p>
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<h5>
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<a name="boost_regex.syntax.basic_extended.h8"></a>
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<span class="phrase"><a name="boost_regex.syntax.basic_extended.character_sets"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.character_sets">Character
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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 [ and ending with ],
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it defines a set of characters, and matches any single character that is
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a member of that set.
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</p>
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<p>
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A bracket expression may contain any combination of the following:
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</p>
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<h6>
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<a name="boost_regex.syntax.basic_extended.h9"></a>
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<span class="phrase"><a name="boost_regex.syntax.basic_extended.single_characters"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.single_characters">Single
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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'.
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</p>
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<h6>
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<a name="boost_regex.syntax.basic_extended.h10"></a>
|
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<span class="phrase"><a name="boost_regex.syntax.basic_extended.character_ranges"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.character_ranges">Character
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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
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POSIX-Extended regular expressions, a character <span class="emphasis"><em>x</em></span> is
|
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within the range <span class="emphasis"><em>y</em></span> to <span class="emphasis"><em>z</em></span>, if it
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collates within that range; this results in locale specific behavior . This
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behavior can be turned off by unsetting the <code class="computeroutput"><span class="identifier">collate</span></code>
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<a class="link" href="../ref/syntax_option_type.html" title="syntax_option_type">option flag</a> - in
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which case whether a character appears within a range is determined by comparing
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the code points of the characters only.
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</p>
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<h6>
|
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<a name="boost_regex.syntax.basic_extended.h11"></a>
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<span class="phrase"><a name="boost_regex.syntax.basic_extended.negation"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.negation">Negation:</a>
|
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</h6>
|
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<p>
|
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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
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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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<h6>
|
|
<a name="boost_regex.syntax.basic_extended.h12"></a>
|
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<span class="phrase"><a name="boost_regex.syntax.basic_extended.character_classes"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.character_classes">Character
|
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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>
|
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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
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<a class="link" href="character_classes.html" title="Character Class Names">character class names</a>.
|
|
</p>
|
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<h6>
|
|
<a name="boost_regex.syntax.basic_extended.h13"></a>
|
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<span class="phrase"><a name="boost_regex.syntax.basic_extended.collating_elements"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.collating_elements">Collating
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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
|
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single character, or any sequence of characters that collates as a single
|
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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
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in the range "ae"-c, assuming that "ae" is treated as
|
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a single collating element in the current locale.
|
|
</p>
|
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<p>
|
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Collating elements may be used in place of escapes (which are not normally
|
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allowed inside character sets), for example <code class="computeroutput"><span class="special">[[.^.]</span><span class="identifier">abc</span><span class="special">]</span></code> would
|
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match either one of the characters 'abc^'.
|
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</p>
|
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<p>
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As an extension, a collating element may also be specified via its <a class="link" 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>
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<p>
|
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matches a NUL character.
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</p>
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<h6>
|
|
<a name="boost_regex.syntax.basic_extended.h14"></a>
|
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<span class="phrase"><a name="boost_regex.syntax.basic_extended.equivalence_classes"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.equivalence_classes">Equivalence
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classes:</a>
|
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</h6>
|
|
<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 class="link" 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, À, Á, Â, Ã, Ä, Å, A, à, á, â, ã, ä and å. Unfortunately implementation
|
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of this is reliant on the platform's collation and localisation support;
|
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this feature can not be relied upon to work portably across all platforms,
|
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or even all locales on one platform.
|
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</p>
|
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<h6>
|
|
<a name="boost_regex.syntax.basic_extended.h15"></a>
|
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<span class="phrase"><a name="boost_regex.syntax.basic_extended.combinations"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.combinations">Combinations:</a>
|
|
</h6>
|
|
<p>
|
|
All of the above can be combined in one character set declaration, for example:
|
|
<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>.
|
|
</p>
|
|
<h5>
|
|
<a name="boost_regex.syntax.basic_extended.h16"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.escapes"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.escapes">Escapes</a>
|
|
</h5>
|
|
<p>
|
|
The POSIX standard defines no escape sequences for POSIX-Extended regular
|
|
expressions, except that:
|
|
</p>
|
|
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
|
|
<li class="listitem">
|
|
Any special character preceded by an escape shall match itself.
|
|
</li>
|
|
<li class="listitem">
|
|
The effect of any ordinary character being preceded by an escape is undefined.
|
|
</li>
|
|
<li class="listitem">
|
|
An escape inside a character class declaration shall match itself: in
|
|
other words the escape character is not "special" inside a
|
|
character class declaration; so <code class="computeroutput"><span class="special">[\^]</span></code>
|
|
will match either a literal '\' or a '^'.
|
|
</li>
|
|
</ul></div>
|
|
<p>
|
|
However, that's rather restrictive, so the following standard-compatible
|
|
extensions are also supported by Boost.Regex:
|
|
</p>
|
|
<h6>
|
|
<a name="boost_regex.syntax.basic_extended.h17"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.escapes_matching_a_specific_char"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.escapes_matching_a_specific_char">Escapes
|
|
matching a specific character</a>
|
|
</h6>
|
|
<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>
|
|
\a
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
'\a'
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
\e
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
0x1B
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
\f
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
\f
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
\n
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
\n
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
\r
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
\r
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
\t
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
\t
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
\v
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
\v
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
\b
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
\b (but only inside a character class declaration).
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
\cX
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
An ASCII escape sequence - the character whose code point is X
|
|
% 32
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
\xdd
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
A hexadecimal escape sequence - matches the single character whose
|
|
code point is 0xdd.
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
\x{dddd}
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
A hexadecimal escape sequence - matches the single character whose
|
|
code point is 0xdddd.
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
\0ddd
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
An octal escape sequence - matches the single character whose code
|
|
point is 0ddd.
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
\N{Name}
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
Matches the single character which has the symbolic name <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.
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
</tbody>
|
|
</table></div>
|
|
<h6>
|
|
<a name="boost_regex.syntax.basic_extended.h18"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.single_character_character_class"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.single_character_character_class">"Single
|
|
character" character classes:</a>
|
|
</h6>
|
|
<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>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">d</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">[[:</span><span class="identifier">digit</span><span class="special">:]]</span></code>
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">l</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">[[:</span><span class="identifier">lower</span><span class="special">:]]</span></code>
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">s</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">[[:</span><span class="identifier">space</span><span class="special">:]]</span></code>
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">u</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">[[:</span><span class="identifier">upper</span><span class="special">:]]</span></code>
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">w</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">[[:</span><span class="identifier">word</span><span class="special">:]]</span></code>
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">D</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">[^[:</span><span class="identifier">digit</span><span class="special">:]]</span></code>
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">L</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">[^[:</span><span class="identifier">lower</span><span class="special">:]]</span></code>
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">S</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">[^[:</span><span class="identifier">space</span><span class="special">:]]</span></code>
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">U</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">[^[:</span><span class="identifier">upper</span><span class="special">:]]</span></code>
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">W</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">[^[:</span><span class="identifier">word</span><span class="special">:]]</span></code>
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
</tbody>
|
|
</table></div>
|
|
<h6>
|
|
<a name="boost_regex.syntax.basic_extended.h19"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.character_properties"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.character_properties">Character
|
|
Properties</a>
|
|
</h6>
|
|
<p>
|
|
The character property names in the following table are all equivalent to
|
|
the names used in character classes.
|
|
</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>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">pX</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
Matches any character that has the property X.
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">[[:</span><span class="identifier">X</span><span class="special">:]]</span></code>
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<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>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
Matches any character that has the property Name.
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">[[:</span><span class="identifier">Name</span><span class="special">:]]</span></code>
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">PX</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
Matches any character that does not have the property X.
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">[^[:</span><span class="identifier">X</span><span class="special">:]]</span></code>
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<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>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
Matches any character that does not have the property Name.
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">[^[:</span><span class="identifier">Name</span><span class="special">:]]</span></code>
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
</tbody>
|
|
</table></div>
|
|
<p>
|
|
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>.
|
|
</p>
|
|
<h6>
|
|
<a name="boost_regex.syntax.basic_extended.h20"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.word_boundaries"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.word_boundaries">Word
|
|
Boundaries</a>
|
|
</h6>
|
|
<p>
|
|
The following escape sequences match the boundaries of words:
|
|
</p>
|
|
<div class="informaltable"><table class="table">
|
|
<colgroup>
|
|
<col>
|
|
<col>
|
|
</colgroup>
|
|
<thead><tr>
|
|
<th>
|
|
<p>
|
|
Escape
|
|
</p>
|
|
</th>
|
|
<th>
|
|
<p>
|
|
Meaning
|
|
</p>
|
|
</th>
|
|
</tr></thead>
|
|
<tbody>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\<</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
Matches the start of a word.
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\></span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
Matches the end of a word.
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">b</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
Matches a word boundary (the start or end of a word).
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">B</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
Matches only when not at a word boundary.
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
</tbody>
|
|
</table></div>
|
|
<h6>
|
|
<a name="boost_regex.syntax.basic_extended.h21"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.buffer_boundaries"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.buffer_boundaries">Buffer
|
|
boundaries</a>
|
|
</h6>
|
|
<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>
|
|
<div class="informaltable"><table class="table">
|
|
<colgroup>
|
|
<col>
|
|
<col>
|
|
</colgroup>
|
|
<thead><tr>
|
|
<th>
|
|
<p>
|
|
Escape
|
|
</p>
|
|
</th>
|
|
<th>
|
|
<p>
|
|
Meaning
|
|
</p>
|
|
</th>
|
|
</tr></thead>
|
|
<tbody>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
\`
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
Matches at the start of a buffer only.
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
\'
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
Matches at the end of a buffer only.
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">A</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
Matches at the start of a buffer only (the same as \`).
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">z</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
Matches at the end of a buffer only (the same as \').
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">Z</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
Matches an optional sequence of newlines at the end of a buffer:
|
|
equivalent 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>
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
</tbody>
|
|
</table></div>
|
|
<h6>
|
|
<a name="boost_regex.syntax.basic_extended.h22"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.continuation_escape"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.continuation_escape">Continuation
|
|
Escape</a>
|
|
</h6>
|
|
<p>
|
|
The sequence <code class="computeroutput"><span class="special">\</span><span class="identifier">G</span></code>
|
|
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>
|
|
<h6>
|
|
<a name="boost_regex.syntax.basic_extended.h23"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.quoting_escape"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.quoting_escape">Quoting
|
|
escape</a>
|
|
</h6>
|
|
<p>
|
|
The escape sequence <code class="computeroutput"><span class="special">\</span><span class="identifier">Q</span></code>
|
|
begins a "quoted sequence": all the subsequent characters are treated
|
|
as literals, until either the end of the regular expression or <code class="computeroutput"><span class="special">\</span><span class="identifier">E</span></code> is found.
|
|
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:
|
|
</p>
|
|
<pre class="programlisting"><span class="special">\*+</span><span class="identifier">a</span>
|
|
<span class="special">\*+</span><span class="identifier">aaa</span>
|
|
</pre>
|
|
<h6>
|
|
<a name="boost_regex.syntax.basic_extended.h24"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.unicode_escapes"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.unicode_escapes">Unicode
|
|
escapes</a>
|
|
</h6>
|
|
<div class="informaltable"><table class="table">
|
|
<colgroup>
|
|
<col>
|
|
<col>
|
|
</colgroup>
|
|
<thead><tr>
|
|
<th>
|
|
<p>
|
|
Escape
|
|
</p>
|
|
</th>
|
|
<th>
|
|
<p>
|
|
Meaning
|
|
</p>
|
|
</th>
|
|
</tr></thead>
|
|
<tbody>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">C</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
Matches a single code point: in Boost regex this has exactly the
|
|
same effect as a "." operator.
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<p>
|
|
<code class="computeroutput"><span class="special">\</span><span class="identifier">X</span></code>
|
|
</p>
|
|
</td>
|
|
<td>
|
|
<p>
|
|
Matches a combining character sequence: that is any non-combining
|
|
character followed by a sequence of zero or more combining characters.
|
|
</p>
|
|
</td>
|
|
</tr>
|
|
</tbody>
|
|
</table></div>
|
|
<h6>
|
|
<a name="boost_regex.syntax.basic_extended.h25"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.any_other_escape"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.any_other_escape">Any
|
|
other escape</a>
|
|
</h6>
|
|
<p>
|
|
Any other escape sequence matches the character that is escaped, for example
|
|
\@ matches a literal '@'.
|
|
</p>
|
|
<h5>
|
|
<a name="boost_regex.syntax.basic_extended.h26"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.operator_precedence"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.operator_precedence">Operator
|
|
precedence</a>
|
|
</h5>
|
|
<p>
|
|
The order of precedence for of operators is as follows:
|
|
</p>
|
|
<div class="orderedlist"><ol class="orderedlist" type="1">
|
|
<li class="listitem">
|
|
Collation-related bracket symbols <code class="computeroutput"><span class="special">[==]</span>
|
|
<span class="special">[::]</span> <span class="special">[..]</span></code>
|
|
</li>
|
|
<li class="listitem">
|
|
Escaped characters <code class="computeroutput"><span class="special">\</span></code>
|
|
</li>
|
|
<li class="listitem">
|
|
Character set (bracket expression) <code class="computeroutput"><span class="special">[]</span></code>
|
|
</li>
|
|
<li class="listitem">
|
|
Grouping <code class="computeroutput"><span class="special">()</span></code>
|
|
</li>
|
|
<li class="listitem">
|
|
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>
|
|
</li>
|
|
<li class="listitem">
|
|
Concatenation
|
|
</li>
|
|
<li class="listitem">
|
|
Anchoring ^$
|
|
</li>
|
|
<li class="listitem">
|
|
Alternation <code class="computeroutput"><span class="special">|</span></code>
|
|
</li>
|
|
</ol></div>
|
|
<h5>
|
|
<a name="boost_regex.syntax.basic_extended.h27"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.what_gets_matched"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.what_gets_matched">What
|
|
Gets Matched</a>
|
|
</h5>
|
|
<p>
|
|
When there is more that one way to match a regular expression, the "best"
|
|
possible match is obtained using the <a class="link" href="leftmost_longest_rule.html" title="The Leftmost Longest Rule">leftmost-longest
|
|
rule</a>.
|
|
</p>
|
|
<h4>
|
|
<a name="boost_regex.syntax.basic_extended.h28"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.variations"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.variations">Variations</a>
|
|
</h4>
|
|
<h5>
|
|
<a name="boost_regex.syntax.basic_extended.h29"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.egrep"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.egrep">Egrep</a>
|
|
</h5>
|
|
<p>
|
|
When an expression is compiled with the <a class="link" href="../ref/syntax_option_type.html" title="syntax_option_type">flag
|
|
<code class="computeroutput"><span class="identifier">egrep</span></code></a> set, then the
|
|
expression is treated as a newline separated list of <a class="link" href="basic_extended.html#boost_regex.posix_extended_syntax">POSIX-Extended
|
|
expressions</a>, a match is found if any of the expressions in the list
|
|
match, for example:
|
|
</p>
|
|
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">regex</span> <span class="identifier">e</span><span class="special">(</span><span class="string">"abc\ndef"</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">egrep</span><span class="special">);</span>
|
|
</pre>
|
|
<p>
|
|
will match either of the POSIX-Basic expressions "abc" or "def".
|
|
</p>
|
|
<p>
|
|
As its name suggests, this behavior is consistent with the Unix utility
|
|
<code class="computeroutput"><span class="identifier">egrep</span></code>, and with grep when
|
|
used with the -E option.
|
|
</p>
|
|
<h5>
|
|
<a name="boost_regex.syntax.basic_extended.h30"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.awk"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.awk">awk</a>
|
|
</h5>
|
|
<p>
|
|
In addition to the <a class="link" href="basic_extended.html#boost_regex.posix_extended_syntax">POSIX-Extended
|
|
features</a> the escape character is special inside a character class
|
|
declaration.
|
|
</p>
|
|
<p>
|
|
In addition, some escape sequences that are not defined as part of POSIX-Extended
|
|
specification are required to be supported - however Boost.Regex supports
|
|
these by default anyway.
|
|
</p>
|
|
<h4>
|
|
<a name="boost_regex.syntax.basic_extended.h31"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.options"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.options">Options</a>
|
|
</h4>
|
|
<p>
|
|
There are a <a class="link" href="../ref/syntax_option_type/syntax_option_type_extended.html" title="Options for POSIX Extended Regular Expressions">variety
|
|
of flags</a> that may be combined with the <code class="computeroutput"><span class="identifier">extended</span></code>
|
|
and <code class="computeroutput"><span class="identifier">egrep</span></code> options when constructing
|
|
the regular expression, in particular note that the <a class="link" href="../ref/syntax_option_type/syntax_option_type_extended.html" title="Options for POSIX Extended Regular Expressions"><code class="computeroutput"><span class="identifier">newline_alt</span></code></a> option alters the syntax,
|
|
while the <a class="link" href="../ref/syntax_option_type/syntax_option_type_extended.html" title="Options for POSIX Extended Regular Expressions"><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</a>
|
|
modify how the case and locale sensitivity are to be applied.
|
|
</p>
|
|
<h4>
|
|
<a name="boost_regex.syntax.basic_extended.h32"></a>
|
|
<span class="phrase"><a name="boost_regex.syntax.basic_extended.references"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.references">References</a>
|
|
</h4>
|
|
<p>
|
|
<a href="http://www.opengroup.org/onlinepubs/000095399/basedefs/xbd_chap09.html" target="_top">IEEE
|
|
Std 1003.1-2001, Portable Operating System Interface (POSIX ), Base Definitions
|
|
and Headers, Section 9, Regular Expressions.</a>
|
|
</p>
|
|
<p>
|
|
<a href="http://www.opengroup.org/onlinepubs/000095399/utilities/grep.html" target="_top">IEEE
|
|
Std 1003.1-2001, Portable Operating System Interface (POSIX ), Shells and
|
|
Utilities, Section 4, Utilities, egrep.</a>
|
|
</p>
|
|
<p>
|
|
<a href="http://www.opengroup.org/onlinepubs/000095399/utilities/awk.html" target="_top">IEEE
|
|
Std 1003.1-2001, Portable Operating System Interface (POSIX ), Shells and
|
|
Utilities, Section 4, Utilities, awk.</a>
|
|
</p>
|
|
</div>
|
|
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
|
|
<td align="left"></td>
|
|
<td align="right"><div class="copyright-footer">Copyright © 1998-2013 John Maddock<p>
|
|
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>)
|
|
</p>
|
|
</div></td>
|
|
</tr></table>
|
|
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