=over

=item $PROGRAM_NAME

=item $0

Contains the name of the program being executed.  On some operating
systems assigning to C<$0> modifies the argument area that the B<ps>
program sees.  This is more useful as a way of indicating the current
program state than it is for hiding the program you're running.
(Mnemonic: same as B<sh> and B<ksh>.)

Note for BSD users: setting C<$0> does not completely remove "perl"
from the ps(1) output.  For example, setting C<$0> to C<"foobar"> will
result in C<"perl: foobar (perl)">.  This is an operating system
feature.

=back