#!/usr/bin/perl

use strict;
no warnings;

foreach my $in (@ARGV){
  my($copy) = "$in.bak";
  copy($in, $copy) or die "File cannot be copied. \n";

  open(INPUT,"$copy") or die 'Cannot open file: $!\n';
  open(OUTPUT,">$in");

  my($replacePattern1) = "foo1";
  ...
  
  
}