[lug] What the heck can I use ${VAR:-} for?

[Zan Lynx]

On Wed, 2008-04-16 at 11:31 -0600, Sean Reifschneider wrote:
> Jeffrey Haemer wrote:
>  >    if [ "${BOOTUP:-}" != "verbose" ]; then
>  >
>  > What's this mean?  Specifically, why's it different from this?
>  >
>  >    if [ "$BOOTUP" != "verbose" ]; then
> 
> There is a mode you can run the shell in, which is off by default, in which
> referencing an unset variable is an error.  The default is that accessing
> an unset variable results in an empty string.  So, if this mode is set,
> doing:
> 
>     [ "$BOOTUP" != verbose ] && echo true
> 
> will result in an error.  Where:
> 
>     [ "${BOOTUP:-}" != verbose ] && echo true
> 
> will not.
> 
> Sean

Hey, neat.  I didn't know shell had that mode.  Since I'm a big fan of
"use strict" in Perl, I believe I'll start adding this to my shell
scripts as well.
-- 
Zan Lynx <zlynx at acm.org>
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