Re: [Help-bash] ${var:?message} customization

[Eric Blake]

On 05/14/2015 06:23 AM, Greg Wooledge wrote:
> If you want to distinguish between "unset" and "set to an empty string",
> you can use a more subtle test:
> 
> if [ "${var+defined}" ]; then

By the way, this test can be portably shortened to:

if [ ${var+y} ]; then

(one of the few places where unquoted variable expansion actually does
the right thing, even on ancient shells)

>     if [ -z "$var" ]; then

Conversely, while this is portable to POSIX shells, it is NOT portable
to some older implementations of /bin/sh (where there are certain values
of $var such as ")" that cause [ to misbehave).


-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

signature.asc
Description: OpenPGP digital signature