In addition to Daedalus207' fix, you are also missing a close paren literal in your subroutine regex:

my $subroutine = qr/((\w+::)*\w+\($sub_args\))/;
#                                           ^
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You might also want to add some optional whitespace at strategic points unless you are striping this first.

Your regex would be easier to read and maintain if you used /x.

my $subroutine = qr/
    (
        (\w+::)*
        \w+
        \(
        $sub_args
        \)
    )
/x;
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