Unix in a Nutshell, 4th Edition

Name

:

Synopsis

    :

Null command. Returns an exit status of 0. See this Example and the ones under case. The line is still processed for side effects, such as variable and command substitutions, or I/O redirection.

Example

Check whether someone is logged in:

    if who | grep $1 > /dev/null
    then :   # Do nothing if user is found
    else echo "User $1 is not logged in"
    fi