POSIX does not define canonical locations of any binaries, not even sh (Ahell & Utilities, sh, Application Usage). Only things that are specified in POSIX by ex

POSIX does not define canonical locations of any binaries, not even sh (Ahell & Utilities, sh, Application Usage). Only things that are specified in POSIX by exact path (Base Definitions, 10.1) are /dev/null, /dev/tty, /dev/console and /tmp. Using /usr/bin/env is common practice, but not standardized in any way. Also, POSIX does not specify the '#!' syntax, and only documents the original mechanism of running shell scripts (execl/vp() passes anything that is not understood by kernel to sh).