To update a file, you open it for reading, read line by line, update the line, and write the line out to a new file. Assume the @table holds the data to add. Then you could use something like

open OLD, "<old.txt" 
   or die "Could not open old.txt: $!";
open NEW, ">new.txt" 
   or die "Could not open new.txt: $!";
my $i = 0;
while (<OLD>) {
   chomp;
   $_ .= $table[ $i++ ];
   print NEW "$_\n";
}
close OLD;
close NEW;
[download]

Nota bene: it is better to entitle your questions with something more descriptive than "file", say, "Editing a file in place", or "Updating a flat file database".

-Mark