luajit is small, fast(well, it can jit), and has a small but complete standard library and can do FFI pretty easily, should be ideal for most homelab usecase

ldd $(which luajit)                                                                                
        linux-vdso.so.1 (0x00007ffee9dc7000)
        libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fb4db618000)
        libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fb4db613000)
        libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007fb4db5f3000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fb4db3ca000)
        /lib64/ld-linux-x86-64.so.2 (0x00007fb4db799000)

Micropython.

I honestly love Powershell, but haven’t tried the Linux version yet. I only use Bash on linux but it has a load of odd quirks that make it unpleasant to use imo. Can’t comment on anything else.

What about Lua/Luajit?

In most scripting languages you have the interpreter binary and the (standard) libraries as separate files. But creating self-extracting executables, that clean up after themselves can easily be done by wrapping them in a shell script.

IMO, if low dependencies and small size is really important, you could also just write your script in a low level compiled language (C, Rust, Zig, …), link it statically (e.g. with musl) and execute that.

Perl is already installed on most linux machines and unless you start delving into module usage, you won’t need to install anything else.

Python is more fashionable, but needs installing on the host and environments can get complicated. I don’t think it scales as well as Perl, if that’s a concern of yours.

Realistically whatever problems you see in python will be there for any other language. Python is the most ubiquitously available thing after bash for a reason.

Also you mentioned provisioning scripts, is that Ansible? If so python is already there, if you mean really just bash scripts I can tell you that does not scale well. Also if you already have some scriptsz what language are they on? Why not write the function there?

Also you’re running syncthing on these machines, I don’t think python is larger than that (but I might be wrong).

If you can, just use Perl. Probably installed on your systems, even the ones without python.

Maybe something like Elvish or Nushell could be worth a look. They have a lot of similarities to classic shells like bash, but an improved syntax and more powerful features. Basically something in between bash and Python. Not sure about disk footprint or general availability/portability though

The smallest footprint for an actual scripting probably will be posix sh - since you already have it ready.

A slightly bigger footprint would be Python or Lua.

If you can drop your requirement for actual scripting and are willing to add a compile step, Go and it’s ecosystem is pretty dang powerful and it’s really easy to learn for small automation tasks.

Personally, with the requirement of not adding too much space for runtimes, I’d write it in go. You don’t need a runtime, you can compile it to a really small zero dependency lib and you have clean and readable code that you can extend, test and maintain easily.

Not quite a scripting language, but I highly recommend you check out cosmo for your usecase. Cosmopolitan, and/or Actually Portable Executable (APE for short) is a project to compile a single binary in such a way that is is extremely portable, and that single binary can be copied across multiple operating systems and it will still just run. It supports, windows, linux, mac, and a few BSD’s.

https://cosmo.zip/pub/cosmos/bin/ — this is where you can download precompiled binaries of certain things using cosmo.

From my testing, the APE version of python works great, and is only 34 megabytes, + 12 kilobytes for the ape elf interpreter.

In addition to python, cosmopolitan also has precompiled binaries of:

• Janet 2.5 MB
• Berry 4.0 MB
• Python 34 MB
• Php 11 MB
• Lua 2.1 MB
• Bash 5.1 MB

And a few more, like tclsh, zsh, dash or emacs (53 MB), which I’m pretty sure can be used as an emacs lisp intepreter.

And it should be noted these may require the ape elf interpeter, which is 12 kilobytes, or the ape assimilate program, which is 476 kilobytes.

EDIT: It also looks like there is an APE version of perl, and the full executable is 24 MB.

EDIT again: I found even more APE/cosmo binaries:

• quickjs (javascript) 2.5 MB
• lisp 20K

I would go with Guile, because it is built-in to the Guix Package Manager which is a really good general-purpose package manager.

It ticks several of your boxes:

• has a CLI interpreter
• is a general purpose language, Scheme, amd compliant with revisions 5, 6, and 7 of the language standard
• allows writing in a functional style (it is one of the original functional programming languages)
• small disk footprint, but still large enough to be “batteries included”
• decent documentation, especially if you use Emacs
• simple setup: not so much, unless you are using Guix to begin with. The standard distribution ships with lots of pre-built bytecode files, you need an installer script to install everything.

It also has pretty good libraries for system maintenance and reporting:

• File-Tree-Walk
• A simple web server
• XML parsing

Why not give (Common)LISP a try?

posix sh + awk for manipulating data?

Python.

Just remember to use pyenv for interpreter installation, version and environment management. It’s pretty straightforward that way and you have predictability.

Don’t ever manually fiddle with the system python and/or libraries or you’ll break your system. You should just rely on the package manager for that.

I don’t know if it matches your desire for easy install of small disk space, but it might make up for it in other arenas - Ruby is my new-found love when making simple scripts. Being able to mostly emulate the shell integration that bash has by just using backticks to call a shell command is the killer feature in my book.