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Groovy supports regular expressions natively using the ~"pattern" expression, which creates a compiled Java Pattern object from the given pattern string. Groovy also supports the =~ (create Matcher) and ==~ (returns boolean, whether String matches the pattern) operators.

For matchers having groups, matcher[index] is either a matched String or a List of matched group Strings.

Since a Matcher coerces to a boolean by calling its find method, the =~ operator is consistent with the simple use of Perl's =~ operator, when it appears as a predicate (in 'if', 'while', etc.). The "stricter-looking" ==~ operator requires an exact match of the whole subject string. It returns a Boolean, not a Matcher.

Regular expression support is imported from Java. Java's regular expression language and API is documented here in the Pattern JavaDocs.

More Examples

Goal: Capitalize words at the beginning of each line:

Goal: Capitalize every word in a string:

Add .toLowerCase() to make the rest of the words lowercase

Gotchas

How to use backreferences with String.replaceAll()

GStrings do not work as you'd expect:

Produces an error like the following:

[] illegal string body character after dollar sign:
solution: either escape a literal dollar sign "\$5" or bracket the value expression "${5}" @ line []

Solution:

Use ' or / to delimit the replacement string:

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2 Comments

  1. An easier way to uppercase all of the first letters. 

    N.B an authentic title case skips prepositions.

    Why use

    ?

    This does the same thing more simply (because we can assume that it.size>0)

  2. Was trying out some of the above code:

    // lets create a Matcher
    def matcher = "cheesecheese" =~ /cheese/
    assert matcher instanceof Matcher

    The assertion statement is always true, no matter what the string or the pattern is set to.

    E.g., this works too
    // lets create a Matcher
    def matcher = "nothing" =~ /cheese/
    assert matcher instanceof Matcher

    Maybe this is the point of the assertion to show that a Matcher is automatically create behind the scenes based on the statement?