use strict;
use warnings;

my @params=qw(input output pattern replacement);
my %settings; @settings{@params}=("0")x @params;
foreach my $key (sort keys %settings) {
    print "$key="; 
    chomp($settings{$key}=<>);
    }
open IN,"<",$settings{input} or die "not a rockstar today"; 

-e $settings{output} and die("File Exists..will not override!")
    or 
open(OUT,">",$settings{output}) or die "Error while opening file: $!";

print OUT map { if(s/$settings{pattern}/$settings{replacement}/g) 
    {$_} else {$_} } (<IN>);

close (IN) and close (OUT);