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	Sun, 27 Apr 1997 06:12:36 +0100 (BST)
To: Curt Sampson <cjs@portal.ca>
Cc: hackers@freebsd.org
Subject: Re: /etc/netstart bogons..
References: <Pine.NEB.3.93.970426214717.24845C-100000@gnostic.cynic.net>
From: Andrew Gierth <andrew@erlenstar.demon.co.uk>
In-Reply-To: Curt Sampson's message of Sat, 26 Apr 1997 21:47:32 -0700 (PDT)
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Date: 27 Apr 1997 06:12:36 +0100
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>>>>> "Curt" == Curt Sampson <cjs@portal.ca> writes:

 >> Can't let this slip past: "" and unset are certainly not the same in sh.

 Curt> So how do we test for the difference between the two?

$ sh
$ if [ -z "${var+X}" ]; then echo "variable 'var' is not set"; fi
variable 'var' is not set
$ var=''
$ if [ -z "${var+X}" ]; then echo "variable 'var' is not set"; fi
$ 

Or, if you want "unset" to be treated like "NO", then

$ unset var
$ echo "value is '${var-NO}'"
value is 'NO'
$ var=''
$ echo "value is '${var-NO}'"
value is ''
$ var='foo'
$ echo "value is '${var-NO}'"
value is 'foo'
$

-- 
Andrew.