The effective uid of this process. Example:
$< = $>;		# set real to effective uid
($<,$>) = ($>,$<);	# swap real and effective uidYou can change both the effective uid and the real uid at the same time by using POSIX::setuid().
(Mnemonic: it's the uid you went to, if you're running setuid.) $< and $> can be swapped only on machines supporting setreuid().