I_pron
would_mod
like_v
to_to
learn_v
this_pron
._sent
OK_ok
?_quest

##</code><code>##

I would like to learn this .
OK ?

##</code><code>##

$DOC1="1.txt";
$DOC2="2.txt";

# Create an associative lookup array from file 1

open (DOC1,$DOC1);
while (<DOC1>) {
  chomp($_);
  $ind = (split /_/)[0];
  $lookup{$ind} = $_;
}
close (DOC1);

open (DOC2,$DOC2);
@lines=<DOC2>;
close (DOC2);

$outln = '';
foreach $line (@lines) {
  @words = split(/ /, $line);
  foreach $word (@words) {
    chomp($word);    # Get rid of stray carriage return
    $outln = $outln . " " . $lookup{$word};
  }
}
print "$outln\n";