Hello,

Stones & Matthew's book Beginning Linux Programming 4/e, chapter 2, "Shell Programming", p50, there is a short explanation about : (null command).

I understand that the null command does nothing and it is also used as true.
But I do not understand the following : construct.

: ${ var:=value }

Perhaps the first ':' means doing nothing, but what is the second ':' followed by '=' ? , and what is ${ } ?

Thanks.

I have found the answer by myself.
The meaning of ":=" is explained at p72.