RegEx - problem with multiline input

Question

I have a String with multiline content and want to select a multiline region, preferably using a regular expression (just because I'm trying to understand Java RegEx at the moment).

Consider the input like:

Line 1
abc START def
Line 2
Line 3
gh END jklm
Line 4

Assuming START and END are unique and the start/end markers for the region, I'd like to create a pattern/matcher to get the result:

 def
Line 2
Line 3
gh

My current attempt is

Pattern p = Pattern.compile("START(.*)END");
Matcher m = p.matcher(input);
if (m.find())
  System.out.println(m.group(1));

But the result is

gh

So m.start() seems to point at the beginning of the line that contains the 'end marker'. I tried to add Pattern.MULTILINE to the compile call but that (alone) didn't change anything.

Where is my mistake?

Matthew Flaschen · Accepted Answer · 2010-09-10 09:05:25Z

8

You want Pattern.DOTALL, so . matches newline characters. MULTILINE addresses a different issue, the ^ and $ anchors.

Pattern p = Pattern.compile("START(.*)END", Pattern.DOTALL);

answered Sep 10, 2010 at 9:05

Matthew Flaschen

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1 Comment

Andreas Dolk Over a year ago

Thanks! Runs like a charm now :)

Jon Freedman · Accepted Answer · 2010-09-10 09:08:26Z

2

You want to set Pattern.DOTALL (so you can match end of line characters with your . wildcard), see this test:

@Test
public void testMultilineRegex() throws Exception {
    final String input = "Line 1\nabc START def\nLine 2\nLine 3\ngh END jklm\nLine 4";
    final String expected = " def\nLine 2\nLine 3\ngh ";
    final Pattern p = Pattern.compile("START(.*)END", Pattern.DOTALL);
    final Matcher m = p.matcher(input);
    if (m.find()) {
        Assert.assertEquals(expected, m.group(1));
    } else {
        Assert.fail("pattern not found");
    }
}

answered Sep 10, 2010 at 9:08

Jon Freedman

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1 Comment

Andreas Dolk Over a year ago

Thanks! Runs like a charm now :)

codaddict · Accepted Answer · 2010-09-10 09:05:09Z

1

The regex metachar . does not match a newline. You can try the regex:

START([\w\W]*)END

which uses [\w\W] in place of ..

[\w\W] is a char class to match a word-char and a non-word-char, so effectively matches everything.

answered Sep 10, 2010 at 9:05

codaddict

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1 Comment

Andreas Dolk Over a year ago

Thanks! In my special case using flag fits slightly better into my existing code, but I'll definitly keep this solution in mind.

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