Re: [PATCH v4 1/2] filter-branch: stop special-casing $filter_subdir argument

Johannes Sixt [off-list ref] 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.