$(

$(

The real gid of this process. If you are on a machine that supports membership in multiple groups simultaneously, gives a space separated list of groups you are in. The first number is the one returned by getgid() , and the subsequent ones by getgroups() , one of which may be the same as the first number.

However, a value assigned to $( must be a single number used to set the real gid. So the value given by $( should not be assigned back to $( without being forced numeric, such as by adding zero. Note that this is different to the effective gid ($) ) which does take a list.

You can change both the real gid and the effective gid at the same time by using POSIX::setgid() . Changes to $( require a check to $! to detect any possible errors after an attempted change.

Mnemonic: parentheses are used to group things. The real gid is the group you left, if you're running setgid.