Also, stop putting your regex pattern in a literal string. i.e. replace

my $regex = 'PATTERN';
s/$regex/.../;
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with

s/PATTERN/.../;
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or

my $regex = qr/PATTERN/;
s/$regex/.../;
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Otherwise you're soon going to run into the different quoting rules between literal strings and literal patterns; e.g. "\bfoo" and qr/\bfoo/ mean two different things.