You are correct. The only time what you need to be worried about missing commands is in special control or embedded systems which have to run ARM or some other super-mini UNIX in a tiny memory.

Really old UNIX systems, say like DGUX, have the commands, too. But they may not work the same as what you expect.

As a more extreme portability note:

Solaris is built to be"aware" of the old-new problem. For example, the default awk on Solaris is old and sometimes awful to use. (use nawk instead). It is retro on purpose. A lot of Solaris shops keep dragging ancient code forward into new versions of Solaris when they upgrade. This means Solaris has to meet the lowest common denominator.
It also does this for executable image files. As long as you keep runtime libraries, ancient executables will run on a modern Solaris box, too.

Newer versions of commands and some BSD leftovers live in a hierarchy of /usr directories (old->newer) /usr/ucb/ (<-this is bsd!) /usr/bin /usr/xpg4/bin /usr/xpg6/bin

So to get modern compliance you need to play with the PATH variable, maybe like this:

Code:

export PATH=/usr/xpg4/bin:/usr/bin:usr/ucb:${PATH}

This allows the whoami command and a modern tr to both work on Solaris.