Re: pg_regress: lookup shellprog in $PATH

I wrote:
> Given the lack of complaints about how pg_ctl works, I'd be inclined
> to follow its lead and just hard-wire "/bin/sh", removing the whole
> SHELLPROG/shellprog dance.  I have not heard of anyone using the
> theoretical ability to compile pg_regress with some other value.

git blame blames that whole mechanism on me: 60cfe25e68d.  It looks
like the reason I did it like that is that I was replacing use of
system(3) with execl(), and system(3) is defined thus by POSIX:

    execl(<shell path>, "sh", "-c", command, (char *)0);

    where <shell path> is an unspecified pathname for the sh utility.

Using SHELL for the "unspecified path" is already a bit of a leap
of faith, since users are allowed to make that point at a non-Bourne
shell.  I don't see any strong reason to preserve that behavior.

            regards, tom lane