Seems, you want to run an external program with the same PID as the parent process?

See exec if you want to terminate the current parent (perl-)process. Here, you can run any kind of program not limited to Perl programs (the original process is lost).

See do (with filenames) and eval for options to run scripts within the same perl instance. However, that obviously doesn't work with non-Perl programs.

BTW, what is PERL? ;-)