#!/usr/bin/perl -w
use strict;

die "must have at least 2 files\n" if @ARGV <2;
my ($first_file, @other_files) = @ARGV;

open(IN, '<', "$first_file") || die "can't open $first_file $!";
while (<IN>)
{
   #work on each line in the first file
}

foreach my $file (@other_files)
{
   open (IN, "<", $file) or die "can't open $file $!";
   while (<IN>)
   {
      #work on each line in the sub files
   }  
}