I think parent means (generally speaking) not to implement larger programs in shell.

If the tasks performed by your program can be expressed maintainably and performantly in shell, go for it.

For programs one size up, something like Perl or Ruby or any other language that allows easy execution of shell commands can be a great solution.

Of course, this all depends on any number of variables. Team competencies, target environments, etc. And with some effort even larger bash scripts can be kept maintainable-ish, and in some target environments (can't always count on other languages being available!) shell scripts might be the only available programming environment.

It depends. I don’t think there is a language which is categorically the best. The solution to a given problem may be harder or easier to express in different languages. Some problems are better solved in C, some in Python, ..., and some in Shell.