How does one handle SIGTERM?

[SirWumpus]

The POSIX signal SIGTERM is the default kill(1) action to terminate a program cleanly; essentially BYE. I do not see a suitable exception code for this. Should the system define one of its own from the reserved system exceptions [-4095..-256]? Or should there be a standard one assigned? Also its behaviour when there is no CATCH frame would be to cleanly exit in the same manner as BYE.

[ruv]

The POSIX signal SIGTERM is the default kill(1) action to terminate a program cleanly;

There is no a standard throw code for this case at the moment, so the system should define own code from the range [-4095..-256].

A standard throw code could be assigned in the future.

Also its behaviour when there is no CATCH frame would be to cleanly exit in the same manner as BYE.

Yes. But the exit status should not be 0 in this case. Probably, it makes sense to always use the throw code as the exit status by default (i.e., unless the program specifies a different value for the exit status using system-specific means).

A Forth system can support a batch mode, which avoids any interaction with the user. In this mode, REPL (interpreting of stdin) should not show a prompt, should output error messages in stderr, and should stop on any uncaught exception. It's convenient to use the throw code as the exit status by default in this mode.

[SirWumpus]

Probably, it makes sense to always use the throw code as the exit status by default

Not practical since the POSIX exit code only uses the 8 least significant bits. Plus the shell will use codes 128+. From NetBSD man exit:

RESTRICTIONS
     Standard C guarantees only that the values zero, EXIT_SUCCESS, and
     EXIT_FAILURE produce meaningful results.  POSIX extends this to guarantee
     that the least significant 8 bits of status are preserved and returned to
     the parent via wait(2).  Values outside the supported range 0-255 are
     bitwise-truncated; therefore, negative values should not be used.

So in light of that I'd probably opt for 1 bye-code in order that pipe is terminated.

[SirWumpus]

I recall the shell using signal number + 128.

[ruv]

Ah, I see. Then, system-defined (or program-defined, if any) set of codes should be used.

[ruv]

I'd probably opt for 1 bye-code in order that pipe is terminated.

"code" have a lot of meanings. Maybe bye-status is better. SP-Forth uses halt ( n -- ⊥ )

[SirWumpus]

I had considered HALT as a name, but felt it might be confused with other uses of halt, ie. halt(1), HLT machine instruction, or HCF. I would have preferred EXIT but that has already been standardised. So I choose to remain close to the BYE name. BYE-STATUS have to think on (exit code vs exit status).