#!/bin/bash

# $0 is visible globally, in functions too

# apparently su -c accepts a command and 1 argument, hence we export
CMDL_ARGS=$@
export CMDL_ARGS

chk_root()
{
    if [[ ! $(id -u) -eq 0 ]]; then
        echo "root user required";
        # exec works similar to fork()
        exec su -c "\"$0\" $CMDL_ARGS"
        exit $?
    fi
}

chk_root $@
if [[ $(id -u) -eq 0 ]]; then
    echo "you're root"
fi