You're right. waitpid(2) does document this. I was also surprised to find that, at least on my linux system, the status integer returned by wait encodes the si

You're right. waitpid(2) does document this. I was also surprised to find that, at least on my linux system, the status integer returned by wait encodes the signal number in the least significant bits and the exit status in the most significant bits. So, when a process dies from SIGPIPE, the status (as set by wait(&status)) is 13; when it does exit(1), it's 256; when it does exit(2), it's 512; when it does exit(3), it's 768, etc. Maybe that encoding was done to avoid misuse from people seeing their exit codes in the raw status returned by wait, and thinking they didn't need to use the macros. In any case, this does mean that, indeed, while the shell does display the same status for both `yes | head -0` and `(exit 141)`, they are in fact different. TIL