The opening parenthesis "(" is special in regular expressions. See perlre. Most likely you want to use quotemeta before interpolating a string into a regular expression, or use \Q...\E like this:

if ($str =~ m/\Q$tr\E/) {
...
};
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For stylistic points, the /g on your regular expression serves no purpose.

To help us help you better, please do not vaguely rephrase Perl error messages but copy and paste the error messages.