perldoc -q contain

Found in /usr/lib/perl5/5.6.0/pod/perlfaq4.pod How can I tell whether a list or array contains a certain element? Hearing the word "in" is an indication that you probably should have used a hash, not a list or array, to store your data...

Populate a hash with the keys as the values of the first column of the first datafile, then loop through the second file and check for the existence of the corresponding number in the hash, as such: (I used pattern matching 'cause that's the first thing that popped into my head, but you can use whatever's best for your particular datafile.)

my %h1;
while (<ONE>) {
  $h1{$1} = $2 if /^(\d)+\s+(.+)/;
}
while (<TWO>) {
  /^(\d)+\s+(.+)/;
  printf "Match: %s\t%s\n", $1, $2 if exists $h1{$1};
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I don't know how efficient this is, but it works. HTH.

--

There are 10 kinds of people -- those that understand binary, and those that don't.