Your questions in the Chatterbox and the ensuing clarification of the problem did make me go back to Mastering Regular Expressions and look up the exact meanings of the /s and /m modifier, thus you get a node here.

In your code, you're trying to match and extract the right data in one go. This can't be done that easily, since Perl only has non-capturing lookahead and there is no lookbehind in Perl (yet). So I use a different approach, capturing the data I want into $1 and then using that to store the address into @addresses.

Update: After amearse updated the data again, I updated my RE a bit, and now it also works with the data as posted. An extended reading of perlre or Mastering Regular Expressions might help here.

#!/usr/bin/perl -w

use strict;

my $i = do { local $/; <DATA> };

my @addresses = ();

while ($i =~ /^From:\s+(.*)$/mg) {
  push @addresses, $1;
};

print join "\n", @addresses;

__DATA__
From:    21755603@ad.cd.net
Date:    Wednesday, April 11, 2001  10:08 PM


From:    21742877@rd.cd.net
Date:    Wednesday, April 11, 2001  07:13 PM

From:    Grouch
Date:    Sunday, February 18, 2001  08:08 AM

#Anything after "Grouch" does not get matched.

From:    21742877@fr.tx.net
Date:    Wednesday, April 11, 2001  07:13 PM
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