#!/usr/bin/perl
$fileName = "abc";

open(IN, "<", "$fileName") or die "Could not open file $fileName";
open(OUT, ">", "$fileName") or die "Could not open file $fileName";
while ($line =(<IN>)) {
$new=$line;
$new =~ s/foo/bar/g;
}
print OUT if $new =~ s/foo/bar/g;