Are you sure it's bash? Most scripts on FreeBSD's are written for sh, which I feel is much more widely supported due to being part of the POSIX standard. Bash is just popular I think.
FreeBSD's /bin/sh is based on ash, like NetBSD's, although I'm not sure how much they have in common these days. dash was forked from NetBSD's version of ash and then simplified considerably and fixed up to be fully (? or at least mostly) POSIX compliant. A while after that NetBSD's shell also had a bunch of POSIX fixes. I'm not sure how FreeBSD's shell is in terms of strict POSIX compliance.
In my opinion, bash has two things (at least vs NetBSD's shell, possibly a few more vs POSIX) that make the average shell script (that I write) much easier. The first is &> which makes it easy to redirect both stdout and stderr to a file for logging. The standard 2>&1 can work but needs to be placed correctly or it doesn't work. That place isn't always the obvious place like it is with &> and running bash seems much preferrable to me than figuring that one out.
The second is ${var@Q} which prints var quoted for the shell, which is nice to use all over the place to make sure any printed file names can be copied and pasted.
My sense is that targeting POSIX is usually done for maximum portability or for use on systems that don't have bash installed by default. However, bash is quite widely available even if not by default and very widely used so I wouldn't say it is unreasonable to look at bash as the de facto standard and POSIX and other shells as being used in more limited circumstances.
I feel like when I see a shell script in my work, which is not in operating systems development of course, people are targeting bash. I agree many things are careful to target sh for certain reasons (e.g. a script that runs in a container where the base image doesn’t have bash installed) but i still think GP’s question is interesting because it’s not common to see, say, a zsh shell script, but seeing #!/bin/bash is super common.
I have done some delightful stuff in `zsh`, but I always lament how slow its numerical array traversal is. Frustratingly, experts told me it really doesn't have to be slow, the devs just don't seem to be bothering to revamp the underlying data structure because they are focusing more on associative arrays.
Bash is pretty much expected to be installed on any Linux distro. On FreeBSD (and likely other BSDs) it is an optional install. If you want a script to run on either, use sh. If strictly Linux, bash is probably safe.
Bash/sh is good for when you need to combine some commands and what needs to be done can be accomplished mostly by CLI commands with a little glue to tie them together. Some times it is surprising what can be accomplished. I wrote a program to import pictures from an SD card on Windows using C#, copying pictures to C:\Pictures\YYYY\MM\DD according to the EXIF data or failing that, file time stamp. I tried to port it to Linux but ran into problems trying to connect to the EXIF library. After struggling with that, I rewrote it using sh, some EXIF tool and various file utilities. It took 31 lines, about half of which were actual commands and the rest comments or white space.
A much bigger project is a script to install Debian with root on ZFS. It's mostly a series of CLI commands with some variable substitution and conditionals depending on stuff like encrypted or not.
> Bash/sh is good for when you need to combine some commands and what needs to be done can be accomplished mostly by CLI commands with a little glue to tie them together.
Once I’ve learned bash, I realised how much more problems i could solve, in addition to a majority of old ones. It’s an entirely new level of “computer literacy”; and a more genuine one.
