Yikes! Where did my parentheses go? So sorry elsiddik, it's really supposed to be:

perl -e 'chdir (shift || "/usr/bin"); system whatis => <*>'
[download]

as long as one-liner is concerned. The chdir functions takes higher precedence than the logical OR (||) operator. The truth is, I added the shift || part later on the textbox without retesting. My fault, my fault....

shmem privately messaged me correcting my answer, and suggested me to have some coffee. But I think I need more than that, perhaps taking a fresh bath :D Thanks, shmem :-)