From mboxrd@z Thu Jan  1 00:00:00 1970
From: Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH v4 1/2] filter-branch: stop special-casing $filter_subdir
 argument
Date: Wed, 11 Nov 2009 10:00:47 -0800
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Cc: Thomas Rast <trast@student.ethz.ch>, git@vger.kernel.org,
	Junio C Hamano <gitster@pobox.com>
To: Johannes Sixt <j.sixt@viscovery.net>
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Johannes Sixt <j.sixt@viscovery.net> writes:

> In the snippet above, dashdash will always be set to "--" because a mere
> '+' in the variable expansion only tests whether the variable ('nonrevs')
> is unset, but it is always set. Even ${nonrevs:+"--"} is wrong, and your
> earlier 'test -z' invocation was the correct way to set dashdash.

I do not mind "test -z", so this is just for information, but you could
use variable substitution with a colon, i.e. ${nonrevs:+"--"}.

IIRC, the colon-form ("do this if unset or empty") wasn't understood by
ancient BSDs but these days it is safe to use.