well here is a quick solution: but be aware there is more then one way to do it :

use strict;

@filelist = ("f1");

while(<DATA>){
  chomp;
  /^([^\t]*)\t/; # I assume it is tab seperated
  my $rec = $1;
  foreach my $file(@filelist){
    my $entry = qx(grep -P "^$rec\t" $file);# I assume it is tab seper
+ated
    print "$rec\t$file\t$entry";
  }
}


__DATA__
K    1
J    2
L    3
H    4
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The cosde is a bit redundant but i'll leave it up to you to clean it up. You can simply redirect the putput to a third file with "perl program.pl > output" or use :

open (OUT, ">", $myoutfile) || die "$!"
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cheers

baxy