You're running into regular expression meta characters, like $. You want to look at perlre and use \Q...\E or quotemeta for interpreting your string as literal characters in regular expression interpolation:

my $regexp = qr/\Qsome$thing\E/;
...
if (/$regexp/) {

[download]

or alternatively

my $regexp = quotemeta('some$thing');
...
if (/$regexp/) {

[download]

In reply to Re: variable interpolation in regexps by Corion
in thread variable interpolation in regexps by Locutus

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