=over =item $EFFECTIVE_USER_ID =item $EUID =item $> X<< $> >> X<$EUID> X<$EFFECTIVE_USER_ID> The effective uid of this process. Example: $< = $>; # set real to effective uid ($<,$>) = ($>,$<); # swap real and effective uid You can change both the effective uid and the real uid at the same time by using POSIX::setuid(). Changes to $> require a check to $! to detect any possible errors after an attempted change. (Mnemonic: it's the uid you went I, if you're running setuid.) C<< $< >> and C<< $> >> can be swapped only on machines supporting setreuid(). =back