For a long while I have had the following >set .PL perl %@execstr[set /v perlparams] >perldebug OFF >set /v perlparams -S >perldebug ON >set /v perlparams -S -d:ptkdb As you can guess perldebug.btm is a script that I use that sets the state of the debug switch for perl. I use the volatile environment to a) make the setting visible across TCC sessions and b) reset to the default when the system is rebooted. This has worked fine up to V10, i.e. >perldebug on >set /v perlparams -S -d:ptkdb >which patren patren is an executable extension : perl %@execstr[set /v perlparams] C:\CMD\patren.pl >patren The ptkdb perl GUI debugger opens with patren.pl loaded In V11 the perl script just runs without the debugger for the exact same sequence. Typing the output of which explicitly at the command line does work in V11.