The : command is often used in
shell scripts to
trap and
ignore signals received by the script.
Thus
trap : 1 2 3 9 15
will cause the
shell ignore any signal 1, 2, 3, or 15 sent to it while executing commands in the script.
Sorry,
Nobody can ignore a signal 9.
Re: ":" and
vi. Technically, ":" is an
escape from the
visual front-end of
vi out to the underlying editing program,
ex. Typing a : inside vi allows you to execute any
ex command. This escape key is a colon because
ex's traditional prompt is a colon.