Wiki: DebugInfo: RegularExpressions

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            [0] => <div class="wikitext"><p class="tightenable top">If you've ever typed &quot;cp *.html ../&quot; at the UNIX command prompt, or entered &quot;garden?&quot; into a web-based search engine, you've already used a simple regular expression. Regular expressions (&quot;regex's&quot; for short) are sets of symbols and syntactic elements used to match patterns of text.</p>
<p class="tightenable">Even these simple examples testify to the power of regular expressions. In the first instance, you've copied all the files which end in &quot;.html&quot; (as opposed to copying them one by one); in the second, you've conducted a search not only for &quot;garden,&quot; but for &quot;garden, gardening, gardens, and gardeners&quot; all at once.</p>
<p class="tightenable bottom">For a tool with full regex support, metacharacters like &quot;*&quot; and &quot;?&quot; (or &quot;wildcard operators,&quot; as they are sometimes called) are only the tip of the iceberg. Using a good regex engine and a well-crafted regular expression, one can easily search through a text file (or a hundred text files) searching for words that have the suffix &quot;.html&quot; (but only if the word begins with a capital letter and occurs at the beginning of the line), replace the .html suffix with a .sgml suffix, and then change all the lower case characters to upper case. With the right tools, this series of regular expressions would do just that:</p>
<pre class="tightenable top bottom">
    s/(^[A_Z]{1})([a-z]+)\.sgml/\1\2\.html/g
    tr/a-z/A-Z/</pre>
<p class="tightenable top">As you might guess from this example, concision is everything when it comes to crafting regular expressions, and while this syntax won't win any beauty prizes, it follows a logical format which you can learn to read and write easily with just a little bit of practice.</p>
<p class="tightenable">Unfortunately, regex syntax and idiosyncracies vary a lot between applications. Even if a regex language looks the same in two different programs, chances are it behaves differently under certain circumstances.</p>
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    [_description] => If you've ever typed "cp *.html ../" at the UNIX command prompt, or entered "garden?" into a web-based search engine, you've already used a simple regular expression. Regular expressions ("regex's" for short) are sets of symbols and syntactic elements used to match patterns of text.
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