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RegExp

matcher.matches() returns false

Why does this code fail?

Code Block
def matcher = "/home/me/script/test.groovy" =~ /\.groovy/
assert matcher.matches()

Because you think you do something like "Oh dear it contains the word!", but you're confusing matches with find

From Javadoc: http://java.sun.com/j2se/1.5.0/docs/api/java/util/regex/Matcher.html#matches()

public boolean matches()
Attempts to match the entire region against the pattern.
...

So "/\.groovy/" is just a subsequence.
You must use

Code Block
def matcher =  "/home/me/script/test.groovy" =~ /.*\.groovy/

What is the difference between =~ and ==~ ?

Pattern, Matcher ?

A pattern is not very useful alone. He's just waiting input to process through a matcher.

Code Block
def pattern =  ~/groovy/
def matcher = pattern.matcher('my groovy buddy')

Matcher can say a lot of thing to you:

  • if the entire input sequence matches the pattern, with matcher.matches() ;
  • if just a subsequence of the input sequence matches the pattern, with matcher.find().

A matcher with /groovy/ pattern finds a matching subsequence in the 'my groovy buddy' sequence.
On the contrary the whole sequence doesn't match the pattern.

Code Block
def m = c.matcher('my groovy buddy')
assert m.find()
assert m.matches() == false

Application: to filter a list of names.

Code Block
def list = ['/a/b/c.groovy', 'myscript.groovy', 'groovy.rc', 'potatoes']
// 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."]

A little tilde headache ? Remember like this

~

the pattern

=~

roughly as the pattern (easy to write)

==~

more than roughly, exactly as the pattern (think hard...)