use strict;
use warnings;
my $file = "file";
open( FILE, "<", $file) or die "$!\n";
$_ = do { local $/; <FILE> };
close(FILE);

s/match/replace/gi;
s/match1/replace1/gi;
open(my $new_file,'>','new_file')or die "$!\n";
print $new_file $_;
close $new_file or die "$!\n";

print `diff $file new_file`;