There is a paragraph, stating:
Perl, Python, Ruby all are really slow compared to statically typed languages. I use Scala for all scripting purposes – it is just as terse as Perl / Python / Ruby but has better collection libraries and runs much, much faster. I’d use Lua if I only needed a thin layer of scripting on top of C/C++. I would use Scala if I only needed a thin layer of C/C++ on the bottom.
IF a new shell is to be designed with scripting functionality, Lua might be a good candidate to be the scripting part and the C++ core to be a shell script engine.
Traditional bash is very powerful, but it is really poor-documented. Thus, writing the bash scripting is extremely difficult if new-comer is involved-in, or if someone stop writing script language for a period of time. For example, I’ve wrote shell script in Linux for two years or so, and I’ve stop writing it one year, meanwhile transforming the platform from mac OSX. When I use the bash script again, the old code is not applicable, for the native code (regular expression using [[ a =~ b ]] syntax), and the difference is merely the “” operator at the regex pattern side. Besides, I use osx and windows at the same time, creating the need to cross-platform scripting.
Therefore, there might be a thought to write a cross-platform shell-engine to take advantage of threading, while scripting language helps to tell what binary to execute.