> This leads to the crux of the matter - I have been told that POSIX > actually requires that all of the commands in this third category (actually > all the sh built-in commands, except the special built-ins) have an > executable that can be subject of an execvp(2) call. The second group > already have that, so it is only the third that matter here. Are we talking about (in POSIX speak) "utilities implemented as a built-in" (as opposed to "built-in utilities" -- which, in turn, differ from "special built-in utilities")? Examples of special built-in utilites are break, return. Examples of (regular) built-in utilities are true, cd. Examples of utilities implemented as a built-in may be echo, printf.
I don't know all of SUSv4tc2 by heart, but the relevant part seems to be 2 Shell Command Language, 2.9 Shell Commands, 2.9.1 Simple Commands, (unnumbered) Command Search and Execution, and then -- 1.d. for built-in utilites -- 1.c/1.e.i.a for utilities implemented as a built-in For (regular) built-in utilities (e.g., cd) I don't see a requirement in 1.d for an executable in PATH. For utilities implemented as a built-in, 1.e.i.a demands the built-in only be used if the path search is successful. A successful path search is defined by "an executable file found", which may refer to the x bit set or "actions equivalent to the execl() function" to succeed (where the distinction is irrelevant due to /usr/bin/printf meeting both requirements). Or are you talking about something completely different? Or a newer SUS?
