Performance wise both can do equally the same, so the question becomes which saves more development time?
Bash relies on calling other commands, and piping them for creating new ones. This has the advantage that you can quickly create new programs just with the code borrowed from other people, no matter what programming language they used.
This also has the side effect of resisting change in sub-commands pretty well, as the interface between them is just plain text.
Additionally Bash is very permissive on how you can write on it. This means it will work well for a wider variety of context, but it also relies on the programmer having the intention of coding in a clean safe manner. Otherwise Bash won't stop you from building a mess.
Python is more structured on style, so a messy programmer won't be as messy. It will also work on operating systems outside Linux, making it instantly more appropriate if you need that kind of portability.
But it isn't as simple for calling other commands. So if your operating system is Unix most likely you will find that developing on Bash is the fastest way to develop.
When to use Bash:
- It's a non graphical program, or the engine of a graphical one.
- It's only for Unix.
When to use Python:
- It's a graphical program.
- It shall work on Windows.
