This is a simple tutorial on how to find out when a variable's value changes without needing prior knowledge of the codebase.

if ( $show_banner == 1 ) {
    print STDERR "$app_name $version ($app_www)\n";
    print STDERR "$copyright $author, $author_email\n\n";
}
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There has to be a faster way to track this variable and I know this is a pretty common problem. So what is the Perl answer you ask? CPAN. There I found the Tie::Trace module.

Tie::Trace allows you to watch a variable and every time the value changes you get a debug message. Here is how I added it to my existing program.

use Tie::Trace qw( watch );

my $show_banner = 1;
watch $show_banner;
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main:: $show_banner => 0 at ./colordiff.pl line 156.
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Now I knew where the value was being changed. From there it was a simple change to an if statement and a rerun of the application test suite to verify no regressions were introduced.

The watch function provided by Tie::Trace does all the heavy lifting by issuing print Dumper statements on the variable as it changes. This is an invaluable tool for following value changes of variables as a program executes.