ALternatively, try

(my $this_proc = $0) =~ s:^.*/::;
[download]

This first copies the old value of $0, the name of the current script (see perlvar), into $this_proc, and then modifies that, deleting everything up to and including the last slash.

BTW Your snippet will fail for filenames like "/foo.pl". To fix it, replace the first plus with a star:

$this_proc = $0 =~ /^.*\/(.+)$/ ? $1 : $0;
[download]