use only posix shell internal commands

[MaxPeal]

use only posix shell internal commands, so it has no longer the need for external progs / commands.

it would be also solve #2 and make #1 easier.

[OneOfTheInfiniteMonkeys]

I agree, good suggestion.

It has been rather a long time since I wrote POSIX compliant scripts. Looking at the internet circa 1995, exciting!
(Repeat comment)