Groovy: Regular Expressions and Multiple Lines

Regular expressions are sometimes used on text that spans multiple lines, which Groovy has support for. I had to search for how to enable multi-line searching, so I thought it would be good to post here.

To allow the expression to span multiple lines we can add (?ms) to the beginning of the expression.

Take the following example, where want to grab the entire book element from a single-line XML document:

    def xml = "<library><book><title>Effective Java</title><author>Bloch</author></book></library>"
    def matcher = xml =~ /<book>.*<\/book>/
    matcher.size() > 0 ? matcher[0] : "NOTHING"

This gives us an entire book:

    <book><title>Effective Java<title><author>Bloch<author><book>

If the XML was to span multiple lines however, we end up with NOTHING:

    def xml = """<library>
      <book>
         <title>Effective Java</title>
         <author>Bloch</author>
      </book>
    </library>"""
    def matcher = xml =~ /<book>.*<\/book>/
    matcher.size() > 0 ? matcher[0] : "NOTHING"

Now if we add the (?ms), we will still get an entire book entry:

    def xml = """<library>
      <book>
         <title>Effective Java</title>
         <author>Bloch</author>
      </book>
    </library>"""
    def matcher = xml =~ /(?ms)<book>.*<\/book>/
    matcher.size() > 0 ? matcher[0] : "NOTHING"

The above results in:

  <book>
    <title>Effective Java<title>
    <author>Bloch<author>
  <book>

If you have any other tips or another way to accomplish the same thing, please feel free to leave a comment.