Paul L. Snyder on 13 Oct 2009 15:39:55 -0700

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Re: [PLUG] Distinguishing between environment variable with null value and one that is not set

On Wed, 14 Oct 2009, sean finney wrote:

> i hate to tell ya, but i'm pretty sure "[[" is also non-posix :)

Few things as a horrible in UNIX as trying to write portable shell scripts.
That's why I don't, I just give dubious advice.  I have good advice, too:
Don't try to write portable shell scripts. ;)

Indeed, '[[' is a reserved word with undefined behavior, as I should have
remembered.  The '[' command works, or its synonym 'test' (which needs a
subshell, so there you have it).

The relevant section of the POSIX spec, for those interested:

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