When I run this script,

#!/usr/bin/perl -w
use strict;

_undef_subroutine();
warn "Got here\n";
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I get this error,

Undefined subroutine &main::_undef_subroutine called at C:\temp\undef.
+pl line 4.
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Are you talking about a checking the syntax without running the script? Komodo has decent syntax checking but I am not sure exactly what you are looking for.

Did you write any tests for your code? If you had it probalbly would have shown up there.