use strict;

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"} || 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: $!";

 while (<IN>) { # 
    s/$settings{"pattern"}/$settings{"replacement"}/g;    
    print OUT $_;
 } # end while

close (IN);
close (OUT);