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POMake a Perl-style regex interpreter behave like a basic or extended regex interpreter
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  1. POMake a Perl-style regex interpreter behave like a basic or extended regex interpreter
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    copied!<p>I am writing a tool to help students learn regular expressions. I will probably be writing it in Java.</p> <p>The idea is this: the student types in a regular expression and the tool shows which parts of a text will get matched by the regex. Simple enough.</p> <p>But I want to support several different regex "flavors" such as:</p> <ul> <li>Basic regular expressions (think: grep)</li> <li>Extended regular expressions (think: egrep)</li> <li>A subset of Perl regular expressions, including the character classes \w, \s, etc.</li> <li>Sed-style regular expressions</li> </ul> <p>Java has the java.util.Regex class, but it supports only Perl-style regular expressions, which is a superset of the basic and extended REs. What I think I need is a way to take any given regular expression and escape the meta-characters that aren't part of a given flavor. Then I could give it to the Regex object and it would behave as if it was written for the selected RE interpreter.</p> <p>For example, given the following regex:</p> <pre><code>^\w+[0-9]{5}-(\d{4})?$ </code></pre> <p>As a basic regular expression, it would be interpreted as:</p> <pre><code>^\\w\+[0-9]\{5\}-\(\\d\{4\}\)\?$ </code></pre> <p>As an extended regular expression, it would be:</p> <pre><code>^\\w+[0-9]{5}-(\\d{4})?$ </code></pre> <p>And as a Perl-style regex, it would be the same as the original expression.</p> <p>Is there a "regular expression for regular expressions" than I could run through a regex search-and-replace to quote the non-meta characters? What else could I do? Are there alternative Java classes I could use?</p>
 

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