Re: Cleaning up background processes

On 10.05.2024 14:35, Geoff Clare wrote:

Janis Papanagnou wrote:
 

But the pseudo-signal 'EXIT' is non-standard (to my knowledge), so you
cannot generally rely on it, depending on your environment, and the OP
asked for a "standard POSIX shell idiom".

 
Quoting POSIX.2-1992, 3.14.13:
 
    The condition can be EXIT; 0 (equivalent to EXIT); or a signal
    specified using a symbolic name, without the SIG prefix, as listed
    in Required Signals and Job Control Signals (Table 3-1 and Table 3-2
    in POSIX.1 {8}). (For example: HUP, INT, QUIT, TERM). Setting a
    trap for SIGKILL or SIGSTOP produces undefined results.
 
It has hardly changed in the current standard (POSIX.1-2017):
 
    The condition can be EXIT, 0 (equivalent to EXIT), or a signal
    specified using a symbolic name, without the SIG prefix, as listed
    in the tables of signal names in the <signal.h> header defined in
    XBD Chapter 13; for example, HUP, INT, QUIT, TERM. Implementations
    may permit names with the SIG prefix or ignore case in signal
    names as an extension. Setting a trap for SIGKILL or SIGSTOP
    produces undefined results.
 

That's good. (And I was obviously misremembering.) Thanks!

BTW, I'm astonished about the "undefined results" for KILL/STOP. Yes,
on OS-level they cannot be caught but why undefined behavior on shell
level; what is the reason or practical rationale for that?

Janis