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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><title>9&nbsp;Regular Expressions</title><link rel="stylesheet" type="text/css" href="../scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="../racket.css" title="default"/><link rel="stylesheet" type="text/css" href="icons.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-style.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../doc-site.css" title="default"/><script type="text/javascript" src="../scribble-common.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../doc-site.js"></script><script type="text/javascript" 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href="other-editors.html" class="tocviewlink" data-pltdoc="x">Command-<wbr></wbr>Line Tools and Your Editor of Choice</a></td></tr><tr><td align="right"></td><td><a href="doc-bibliography.html" class="tocviewlink" data-pltdoc="x">Bibliography</a></td></tr><tr><td align="right"></td><td><a href="doc-index.html" class="tocviewlink" data-pltdoc="x">Index</a></td></tr></table></div></div><div class="tocviewlist"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,&quot;tocview_1&quot;);">&#9660;</a></td><td>9&nbsp;</td><td><a href="" class="tocviewselflink" data-pltdoc="x">Regular Expressions</a></td></tr></table><div class="tocviewsublistbottom" style="display: block;" id="tocview_1"><table cellspacing="0" cellpadding="0"><tr><td align="right">9.1&nbsp;</td><td><a href="regexp-intro.html" class="tocviewlink" data-pltdoc="x">Writing Regexp Patterns</a></td></tr><tr><td align="right">9.2&nbsp;</td><td><a href="regexp-match.html" class="tocviewlink" data-pltdoc="x">Matching Regexp Patterns</a></td></tr><tr><td align="right">9.3&nbsp;</td><td><a href="regexp-assert.html" class="tocviewlink" data-pltdoc="x">Basic Assertions</a></td></tr><tr><td align="right">9.4&nbsp;</td><td><a href="regexp-chars.html" class="tocviewlink" data-pltdoc="x">Characters and Character Classes</a></td></tr><tr><td align="right">9.5&nbsp;</td><td><a href="regexp-quant.html" class="tocviewlink" data-pltdoc="x">Quantifiers</a></td></tr><tr><td align="right">9.6&nbsp;</td><td><a href="regexp-clusters.html" class="tocviewlink" data-pltdoc="x">Clusters</a></td></tr><tr><td align="right">9.7&nbsp;</td><td><a href="regexp-alternation.html" class="tocviewlink" data-pltdoc="x">Alternation</a></td></tr><tr><td align="right">9.8&nbsp;</td><td><a href="Backtracking.html" class="tocviewlink" data-pltdoc="x">Backtracking</a></td></tr><tr><td align="right">9.9&nbsp;</td><td><a href="Looking_Ahead_and_Behind.html" class="tocviewlink" data-pltdoc="x">Looking Ahead and Behind</a></td></tr><tr><td align="right">9.10&nbsp;</td><td><a href="An_Extended_Example.html" class="tocviewlink" data-pltdoc="x">An Extended Example</a></td></tr></table></div></div></div></div><div class="maincolumn"><div class="main"><div class="navsettop"><span class="navleft"><form class="searchform"><input class="searchbox" style="color: #888;" type="text" value="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, &quot;6.1&quot;, &quot;../&quot;);" onfocus="this.style.color=&quot;black&quot;; this.style.textAlign=&quot;left&quot;; if (this.value == &quot;...search manuals...&quot;) this.value=&quot;&quot;;" onblur="if (this.value.match(/^ *$/)) { this.style.color=&quot;#888&quot;; this.style.textAlign=&quot;center&quot;; this.value=&quot;...search manuals...&quot;; }"/></form>&nbsp;&nbsp;<a href="../index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot(&quot;6.1&quot;);">top</a></span><span class="navright">&nbsp;&nbsp;<a href="io-patterns.html" title="backward to &quot;8.6 I/O Patterns&quot;" data-pltdoc="x">&larr; prev</a>&nbsp;&nbsp;<a href="index.html" title="up to &quot;The Racket Guide&quot;" data-pltdoc="x">up</a>&nbsp;&nbsp;<a href="regexp-intro.html" title="forward to &quot;9.1 Writing Regexp Patterns&quot;" data-pltdoc="x">next &rarr;</a></span>&nbsp;</div><h3 x-source-module="(lib &quot;scribblings/guide/guide.scrbl&quot;)" x-part-tag="&quot;regexp&quot;">9<tt>&nbsp;</tt><a name="(part._regexp)"></a>Regular Expressions</h3><blockquote class="refpara"><blockquote class="refcolumn"><blockquote class="refcontent"><p>This chapter is a modified version of [<a href="doc-bibliography.html#%28cite._.Sitaram05%29" data-pltdoc="x">Sitaram05</a>].</p></blockquote></blockquote></blockquote><p>A <a name="(tech._regexp)"></a><span style="font-style: italic">regexp</span> value encapsulates a pattern that is described by a
string or <a href="bytestrings.html#%28tech._byte._string%29" class="techoutside" data-pltdoc="x"><span class="techinside">byte string</span></a>.  The regexp matcher tries to match this
pattern against (a portion of) another string or byte string, which we
will call the <a name="(tech._text._string)"></a><span style="font-style: italic">text string</span>, when you call functions like
<span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&amp;rel=regexp.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._regexp-match%2529%2529&amp;version=6.1" class="RktValLink Sq" data-pltdoc="x">regexp-match</a></span>.  The text string is treated as raw text, and
not as a pattern.</p><table cellspacing="0" cellpadding="0"><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="regexp-intro.html" class="toclink" data-pltdoc="x">9.1<span class="hspace">&nbsp;</span>Writing Regexp Patterns</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="regexp-match.html" class="toclink" data-pltdoc="x">9.2<span class="hspace">&nbsp;</span>Matching Regexp Patterns</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="regexp-assert.html" class="toclink" data-pltdoc="x">9.3<span class="hspace">&nbsp;</span>Basic Assertions</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="regexp-chars.html" class="toclink" data-pltdoc="x">9.4<span class="hspace">&nbsp;</span>Characters and Character Classes</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="regexp-chars.html#%28part._.Some_.Frequently_.Used_.Character_.Classes%29" class="toclink" data-pltdoc="x">9.4.1<span class="hspace">&nbsp;</span>Some Frequently Used Character Classes</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="regexp-chars.html#%28part._.P.O.S.I.X_character_classes%29" class="toclink" data-pltdoc="x">9.4.2<span class="hspace">&nbsp;</span>POSIX character classes</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="regexp-quant.html" class="toclink" data-pltdoc="x">9.5<span class="hspace">&nbsp;</span>Quantifiers</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="regexp-clusters.html" class="toclink" data-pltdoc="x">9.6<span class="hspace">&nbsp;</span>Clusters</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="regexp-clusters.html#%28part._.Backreferences%29" class="toclink" data-pltdoc="x">9.6.1<span class="hspace">&nbsp;</span>Backreferences</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="regexp-clusters.html#%28part._.Non-capturing_.Clusters%29" class="toclink" data-pltdoc="x">9.6.2<span class="hspace">&nbsp;</span>Non-capturing Clusters</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="regexp-clusters.html#%28part._regexp-cloister%29" class="toclink" data-pltdoc="x">9.6.3<span class="hspace">&nbsp;</span>Cloisters</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="regexp-alternation.html" class="toclink" data-pltdoc="x">9.7<span class="hspace">&nbsp;</span>Alternation</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="Backtracking.html" class="toclink" data-pltdoc="x">9.8<span class="hspace">&nbsp;</span>Backtracking</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="Looking_Ahead_and_Behind.html" class="toclink" data-pltdoc="x">9.9<span class="hspace">&nbsp;</span>Looking Ahead and Behind</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="Looking_Ahead_and_Behind.html#%28part._.Lookahead%29" class="toclink" data-pltdoc="x">9.9.1<span class="hspace">&nbsp;</span>Lookahead</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="Looking_Ahead_and_Behind.html#%28part._.Lookbehind%29" class="toclink" data-pltdoc="x">9.9.2<span class="hspace">&nbsp;</span>Lookbehind</a></p></td></tr><tr><td><p><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><a href="An_Extended_Example.html" class="toclink" data-pltdoc="x">9.10<span class="hspace">&nbsp;</span>An Extended Example</a></p></td></tr></table><blockquote class="refpara"><blockquote class="refcolumn"><blockquote class="refcontent"><p><span class="imageleft"><img src="magnify.png" alt="+" width="24" height="24"/></span><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&amp;rel=regexp.html&amp;version=6.1" class="Sq" data-pltdoc="x">Regular Expressions</a> in <a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&amp;rel=index.html&amp;version=6.1" class="Sq" data-pltdoc="x"><span style="font-weight: bold">The Racket Reference</span></a> provides more on regexps.</p></blockquote></blockquote></blockquote><div class="navsetbottom"><span class="navleft"><form class="searchform"><input class="searchbox" style="color: #888;" type="text" value="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, &quot;6.1&quot;, &quot;../&quot;);" onfocus="this.style.color=&quot;black&quot;; this.style.textAlign=&quot;left&quot;; if (this.value == &quot;...search manuals...&quot;) this.value=&quot;&quot;;" onblur="if (this.value.match(/^ *$/)) { this.style.color=&quot;#888&quot;; this.style.textAlign=&quot;center&quot;; this.value=&quot;...search manuals...&quot;; }"/></form>&nbsp;&nbsp;<a href="../index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot(&quot;6.1&quot;);">top</a></span><span class="navright">&nbsp;&nbsp;<a href="io-patterns.html" title="backward to &quot;8.6 I/O Patterns&quot;" data-pltdoc="x">&larr; prev</a>&nbsp;&nbsp;<a href="index.html" title="up to &quot;The Racket Guide&quot;" data-pltdoc="x">up</a>&nbsp;&nbsp;<a href="regexp-intro.html" title="forward to &quot;9.1 Writing Regexp Patterns&quot;" data-pltdoc="x">next &rarr;</a></span>&nbsp;</div></div></div><div id="contextindicator">&nbsp;</div></body></html>