in reply to Re^2: debugger switch
in thread debugger switch

Try this:

    perl <program>

The -d switch is invoking the debugger. No switch, no debugger.

UPDATE: Read perlvar and pay particular attention to the built-in variables $DEBUGGING ($^D) and $PERLDB ($^P). (Sorry, I initially misread your question.)

In Section Seekers of Perl Wisdom