Support POSIX

[bharatvaj]

I use busybox-w32 which emulates a constrained UNIX environment in Windows, the silver lining
being that the scripts that work in this environment are extremely portable.
I tested this with MinGW, FreeBSD, Ubuntu and Alpine each with different shells and they all seem to work.

I deleted this check, as this script should work if there is sh installed in the system.

    echo "Oups, I cannot identify your current OS."
    echo "Please open a ticket or a pull request so we can add your OS to the list of supported systems."
    exit 1

I had to remove null terminated command args as it is not possible to store null
terminated strings in variables and calling the commands multiple times were slowing down the script.

I removed python dependency by emulating the feature with shell's pattern substitution, and awk by
combining tr with wc.