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<h2>RegExp</h2><h3>matcher.matches() returns false</h3><p>Why does this code fail?</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>def matcher = "/home/me/script/test.groovy" =~ /\.groovy/
assert matcher.matches()
</pre></td></tr></table><p>Because you think you do something like <em>&quot;Oh dear it contains the word!&quot;</em>, but you're confusing <em>matches</em> with <em>find</em></p><p>From Javadoc: <a href="http://java.sun.com/j2se/1.5.0/docs/api/java/util/regex/Matcher.html#matches()">http://java.sun.com/j2se/1.5.0/docs/api/java/util/regex/Matcher.html#matches()</a></p><p><span style="color: blue;">public boolean matches()</span><br /> <span style="color: blue;">Attempts to match the</span> <span style="color: red;"><strong>entire</strong></span> <span style="color: blue;">region against the pattern.</span><br /> <span style="color: blue;">...</span></p><p>So &quot;<em>/\.groovy/</em>&quot; is just a subsequence.<br /> You must use</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>def matcher =  "/home/me/script/test.groovy" =~ /.*\.groovy/
</pre></td></tr></table><h3>What is the difference between =~ and ==~ ?</h3><ul><li>~ is the <a href="http://java.sun.com/j2se/1.5.0/docs/api/java/util/regex/Pattern.html">Pattern</a> symbol.</li><li>=~ means <a href="http://java.sun.com/j2se/1.5.0/docs/api/java/util/regex/Matcher.html#find()">matcher.find()</a></li><li>==~ means <a href="http://java.sun.com/j2se/1.5.0/docs/api/java/util/regex/Matcher.html#matches()">matcher.matches()</a></li></ul><h4>Pattern, Matcher ?</h4><p>A pattern is not very useful alone. He's just waiting input to process through a <em>matcher</em>.</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>def pattern =  ~/groovy/
def matcher = pattern.matcher('my groovy buddy')
</pre></td></tr></table><p>Matcher can say a lot of thing to you:</p><ul><li>if the <em>entire</em> input sequence matches the pattern, with <code><a href="http://java.sun.com/j2se/1.5.0/docs/api/java/util/regex/Matcher.html#matches()">matcher.matches()</a></code> ;</li><li>if just a <em>subsequence</em> of the input sequence matches the pattern, with <code><a href="http://java.sun.com/j2se/1.5.0/docs/api/java/util/regex/Matcher.html#find()">matcher.find()</a></code>.</li></ul><p>A matcher with /groovy/ pattern <strong>finds</strong> a matching subsequence in the 'my groovy buddy' sequence.<br /> On the contrary the whole sequence doesn't <strong>match</strong> the pattern.</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>def m = c.matcher('my groovy buddy')
assert m.find()
assert m.matches() == false
</pre></td></tr></table><p>Application: to filter a list of names.</p><table class="wysiwyg-macro" data-macro-name="code" data-macro-parameters="language=groovy" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGU6bGFuZ3VhZ2U9Z3Jvb3Z5fQ&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>def list = ['groovy', '/a/b/c.groovy', 'myscript.groovy', 'groovy.rc', 'potatoes', 'groovy.']
// find all items whom a subsequence matches /groovy/
println list.findAll{ it =~ /groovy/ }  // => [ "groovy", "/a/b/c.groovy", "myscript.groovy", "groovy.rc", "groovy." ]

// find all items who match exactly /groovy/
println list.findAll{ it ==~ /groovy/ } // => [ "groovy" ]

// find all items who match fully /groovy\..*/ ('groovy' with a dot and zero or more char trailing)
println list.findAll{ it ==~ /groovy\..*/ } // => ["groovy.rc", "groovy."]
</pre></td></tr></table><p>A little tilde headache ? Remember like this</p><table class="confluenceTable"><tbody><tr><td class="confluenceTd"><p>~</p></td><td class="confluenceTd"><p>the pattern</p></td></tr><tr><td class="confluenceTd"><p>=~</p></td><td class="confluenceTd"><p>roughly as the pattern (easy to write)</p></td></tr><tr><td class="confluenceTd"><p>==~</p></td><td class="confluenceTd"><p>more than roughly, <strong>exactly</strong> as the pattern (think hard...)</p></td></tr></tbody></table>