Changing "sed -E" to "sed -r" and all instances of "==" to "=" makes this script run on my Debian system. Unfortunately, it leaves the terminal blue when it is done.
If you add a line like the following to the end of the script, any color changes should be undone:
echo "\033[0m"
Also, I believe Debian's /bin/sh is "dash" whereas it is "bash" on most other systems. You could change your copy of the script's header to use "/bin/bash" instead of "sh" (assuming that bash is installed too), which is easier than fixing equal-signs and such.
As far as the original code is concerned, using "perl" may be slightly more portable than "sed -E".
As far as the original code is concerned, using "perl" may be slightly more portable than "sed -E".