>     ENV=$HOME/.shrc; export ENV
...
>     PS1="$(hostname -s)"
>     if [ -x /usr/bin/id -a $(/usr/bin/id -u) -eq 0 ]; then
>             PS1="$PS1 # "
>     else
>             PS1="$PS1 $ "
>     fi

Ignoring the obvious errors, there are two problem with this:

1) It causes 2 other programs to be started up *every* time sh(1) is
   run.  Consider the effect of this on a `make build' on a VAX.  The
   performance loss can be measured in hours, maybe even days.

2) There is absolutely no reason to do something that complicated.
   Just save the host name in a variable and concatenate the default
   PS1 (in the same way as my code does) in `.shrc'.

Why make the problem harder than it actually is??