in reply to my code works just fine, but how :D

All the lines will end in a new line. But you're seeding @comp with a string that doesn't have a newline. So, on the first run, the only way you get a match if your file contains 4 characters: s, e, e and d, and no newline.

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Re^2: my code works just fine, but how :D
by ikegami (Patriarch) on Apr 25, 2012 at 17:00 UTC
    Not true. A first line of "|\n" would also match, for example. Fix: 
    my @comp = "seed\n";                                # Fix 1 
while ($line = <>) {
   push(@comp, $line);
   print $line if $comp[0] =~ /^\Q$comp[1]\E\z/;    # Fix 2
   shift(@comp);
}

    [download]

    But why not just use eq? 

    my @comp = "seed\n"; 
while ($line = <>) {
   push(@comp, $line);
   print $line if $comp[0] eq $comp[1];
   shift(@comp);
}

    [download]

    Simpler still: 

    my $last = ""; 
while (<>) {
   print if $_ eq $last;
   $last = $_;
}

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