On Wed, Aug 14, 2019 at 5:41 PM Lassi Kortela <xxxxxx@lassi.io> wrote:

Is 128 fully portable? For the longest time, I thought the safe portable
maximum was 126 (with 127 reserved for some kind of abnormal
termination) but that information may be more than a decade old. Current
safe range would seem to be 0..255, I can't find any concrete exceptions
to that rule.

The exit and wait procedures support 0-255, no problem.  However, when a process running in the shell dies on a signal, the variable $? is set to 128 plus the signal number.  Consequently, these two exit situations are indistinguishable to the shell:

$ (exit 129); echo $?
$ sh -c '/bin/kill 1 $$'; echo $?

This only affects shell scripts that actually examine $?.  In 30+ years of shell programming I have never done so that I can remember.

I think exit code 1 ("catchall for general errors") is the right mapping for #f.  It is also what Chibi uses on both *ix and Windows.  (On Plan 9 Chibi translates #f to "chibi error" and #t to "".)

John Cowan          http://vrici.lojban.org/~cowan        xxxxxx@ccil.org
You annoy me, Rattray!  You disgust me! You irritate me unspeakably!
Thank Heaven, I am a man of equable temper, or I should scarcely be able
to contain myself before your mocking visage.  --Stalky imitating Macrea