[sf-lug] Fwd: [UMALUG] bash scripting question

Rick Smith rick at rbsmith.com
Fri Mar 7 19:36:29 PST 2008

jim stockford wrote:
 >     i've always viewed the  :  command as a no op
 > (aka nop).
 >     even after reading and pondering, i cannot figure
 > out a use other than perhaps as a placeholder, but
 > a comment seems a much more useful placeholder.
 >     what is a good reason for putting the  :  command
 > in a shell script?

The case where I've seen is to define an env variable
if not defined:

   : ${FOO=bar}

My understanding is this will leave FOO alone if
defined or set it to bar if not.  The : is needed
because the expression also returns a value which
gets run, but as an option to :, it does nothing.


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