How do you deal with it, when you are writing bash scripts?
In bash, `eval` is a footgun like any other. You can use it, but you just need to be aware of where your toes are when it shoots.
It's usually a "bad idea" in the sense that if you think you need to use it, you probably don't, and 90% of the time, there is an easier way to accomplish what you want to do. The next 5% of the time, using `eval` might be easier but will also create maintenance debt with its overgeneralization. And the final 5% of the time might be actual legit use cases for `eval`.
I just grepped my codebase for `eval` and I almost never use it. One example of the "overgeneralized" 5% might be when I realized I could use `eval` to set "variable variables" (i.e. the name of the variable is itself a variable, taken from a function argument). It was cool, but I ended up deleting it in favor of a more concrete solution.
Personally, if I'm hesitating to use `eval`, it's usually not for any security reasons. In general, my bash scripts only exist in dev machines and CI runners, and I don't copy them into the application containers that are exposed to a live runtime environment with untrusted users. So for CI/dev scripts, I can safely assume the code will only run in CI/dev, and therefore I can trust arbitrary user input (which I can of course still validate).
This is the real code that a Ansible uses to run a shell command correctly and is 350 lines and is still a small subset of the features of a single line of bash. https://github.com/ansible/ansible/blob/a2776443017718f6bbd8...
The Python code to do what a single mv invocation does is 120 lines https://github.com/ansible/ansible/blob/a2776443017718f6bbd8...
People always focus on the footguns that exist in Bash the language but ignore how much systems programming is abstracted away from you in the shell environment.
In Bash you can enter a Linux namespace with a single nsenter invocation. If you want to do the same in Python you have use ctypes and call libc.clone manually.
Python has shutil.move and os.rename but the Ansible example is to illustrate that there's a lot of code that needs to surround those calls to make them useful and they're not 1-1.
- it's portable accross OSes (and keep flags if the OS supports it, deal with encoding, etc)
- it ensures selinux context is saved if there is such a thing
- it has proper and rich error communication with the calling code
- it's includes documentation and comments
- it outputs json par parsing and storage
No to say "mv" is not awesome, because it is. There is much more boiler plate in python, and is why I'll often do subprocess.check_call(['mv', 'src', 'dst']) if my script is linux only.
But you are pushing it
By the way, I don't know if this is the canonical implementation, but FreeBSD mv is 481 lines of C: https://github.com/freebsd/freebsd-src/blob/master/bin/mv/mv...