A tale 1/2:
/bin/true in XENIX (and probably elsewhere) is probably the shortest UNIX program.
It is 0 bytes long. Zero.
On a GNU/Linux system, /bin/true is a dynamically linked binary, implemented in C, linked to libc, calling 13 different system calls, consuming three times as much memory as the whole XENIX system.
A tale 2/2:
Anyhow, the C version on either XENIX or GNU/Linux is actually much faster than the zero-length one. That's because a program with neither a shebang nor an executable header is historically considered a shell script. And thus, /bin/sh is launched to interpret a the zero-length /bin/true.
Morale: None. It's actually a pretty stupid story, perhaps also wrong in some important aspect.
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