On Tue, Aug 17, 2021 at 07:30:45AM -0700, L A Walsh wrote:
> The pairs are about 4 related operations. If you let P = the oPerator
> then the odd lines are about ':P' and the even lines are about 'P' (no
> colon).
> The Pairs from 1-4 are about the operators: '-', '=', '?', '+'
>
> Pair 4 shows effects of ':+' and '+'.
>
> Isn't that what you are talking about?
>
> Yeah -- w/o the ':' looks a bit 'off', but it has a separate meaning
> and has been around for a long time.
>
> (I first encountered it when porting 1980's era scripts)
The form without the colon (':') is the original form, and comes from
the Bourne shell. If you read sufficiently old literature, you'll see
*only* those forms mentioned.
The form with the colon was added by the first Korn shell, and became
widely adopted by other shells. Eventually it became standardized
in POSIX.
So yes, all 8 forms are standardized by POSIX.
I'm still wondering what issue the OP is actually seeing. If they claim
that changing ${GCC+-stuff} to ${GCC:+-stuff} in some file fixes things,
and if they also claim that *something* is setting the GCC variable to
the empty string rather than unsetting it, then perhaps it's not a
syntactic error at all, but rather a logical error.
Either the thing that's setting GCC to the empty string ought to be
changed to unset GCC, or else the ${GCC+-stuff} check ought to be changed
to ${GCC:+-stuff} (at the risk of breaking Bourne shell compatibility,
if we care about that).
But this is speculative until they tell us what the actual problem is.
