Re: regex backreference

[Kenosis]

Perhaps the following will be helpful:

use strict;
use warnings;

my %seen;
while (<DATA>) {
    !$seen{ $. . $1 }++ and print "Line $.: $1\n"
      while /(\b\w{3}\b)(?=.*\1)/g;
}

__DATA__
foofoo
foo foo
foo bar foo
foo bar foo bar
foooof
foo oof
foo and bar
foo foo and and bar bar
foo and bar foo and bar
and or and or say or say or say or say

Output:

Line 2: foo
Line 3: foo
Line 4: foo
Line 4: bar
Line 8: foo
Line 8: and
Line 8: bar
Line 9: foo
Line 9: and
Line 9: bar
Line 10: and
Line 10: say