Thank you, still new here so I was not aware. So I've gone through and made the changes you've suggested. However, nothing happens with my output.txt file once the code is executed. 
use strict;
use warnings;

open(my $in, "<", "input.txt")
    or die "Cannot open < input.txt: $!";

open(my $out, ">", "output.txt")
    or die "Cannot open < output.txt: $!";

while(my $line = <$in>) {
    $line =~ s/new/old/i;
    print $out $line;
}

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In reply to Re^2: [Class Assignment] Regex and Output Files by Hayest
in thread [Class Assignment] Regex and Output Files by Hayest

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