$(shell ...) exit status

[David Boyce]

How does one determine the exit status of the shell forked by $(shell
...)? I see nothing about it in the 3.81 online manual. I need to run
a command for which the null string is a perfectly legal
output value, so I can't get away with anything like this:

foo     :=      $(shell mycommand)

ifeq($foo),)
<code to handle error conditions>
endif

And I don't just need to abort on error either. If the command fails I
have another (slower and less reliable) way to get the data whereas if
it succeeds with null output I want to continue on happily. Which
means I need exit status. Is this an oversight in the spec?

Thanks,
David Boyce