> If a command is not found, the exit status shall be 127. If the
> command name is found, but it is not an executable utility, the exit
> status shall be 126. Applications that invoke utilities without using
> the shell should use these exit status values to report similar errors.
[1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_08_02
