Date: Fri, 13 Jul 2001 21:16:11 -0000
From: cberry@cinenet.net (Craig Berry)
Subject: Re: regexp question
Message-Id: <tkup8rq30etpb0@corp.supernews.com>

Matt D (emdee@DEMUNGEcwcom.net) wrote:
: there's probably a 'doh! of course!' answer to this, but it's eluding
: me at the moment...
: 
: i want to capture a keyword and up to 3 words either side of it from a
: block of text (keyword could potentially be at the beginning, end or
: anywhere in the middle).
: 
: my block of text is a single space-delimited list of words.

If the block isn't big and exact spacing doesn't need to be maintained,
I'd do it like this:

  my $block = 'foo blah barg zneeb foo dribble foo glarb doh foo sneex';
  my $kw    = 'foo';
  my @words = $block =~ /(\w+)/g;

  for (my $i = 0; $i < @words; $i++) {
    if ($words[$i] eq $kw) {
      my $lo = $i - 3;
      my $hi = $i + 3;
      $lo = 0       if $lo < 0;
      $hi = $#words if $hi > $#words;
      print join(' ', @words[$lo..$hi]), "\n";
    }
  }

This grabs every instance of 'foo' and up to three words on either side of
it.  Note that overlapping ranges will work properly.

-- 
   |   Craig Berry - http://www.cinenet.net/~cberry/
 --*--  "Brute force done fast enough looks slick."
   |             - William Purves