Very Computer

by **wayne t. wats** » Fri, 13 Jun 1997 04:00:00

"Progress might have been all right once but it has gone on
far too long." Ogden Nash

by **Brendan O'D** » Fri, 13 Jun 1997 04:00:00

Quote:>That's the question. Is unset x
>the same as x="" when using the Korn shell?

Depends what you are doing with $x. When you use unset, you remove
the variable entirely, x= retains the variable but sets it to nothing.

As far as scripting is concerned, the constructs such as

[[ -n $x ]] and [[ -z $x ]]

should work the same either way. There is a difference for parameter
substitutions, where constructs such as:

${x-whatever}
${x:-whatever}

will substitute `whatever' in both cases for `unset x', but only in
the second (:) case for `x='.

Regards,
--

Compusol Pty. Limited (NSW, Australia) +61 2 9809 0133

by **Steffen Klu** » Fri, 13 Jun 1997 04:00:00

Quote:>That's the question. Is unset x
>the same as x="" when using the Korn shell?

No. `unset x' removes the shell variable x, whereas
`x=""' sets it to "" (the empty string). You can
easily verify this:

set -u (or set -o nounset)
x=""
echo $x
unset x
echo $x

Hope this helps
Steffen.

--

Fujitsu Australia Ltd
Keywords: photography, Mozart, UNIX, Islay Malt
--

by **Michael We** » Sat, 14 Jun 1997 04:00:00

Hallo wayne, zu "ksh: unset x same as x=""?" vom 12.06.97:

wtw>That's the question. Is unset x
wtw>the same as x="" when using the Korn shell?

No. With "unset" you delete the variable. With x="" you define a variable,
the value is a nullstring.

In korn shell it is the same thing in most cases, if you get the value of
an unset variable, you will get no error. With the shell option

set -o nounset

you will get an error, if the variable is not defined.

Gruss, Michael