Rather than just structural colouring (params are colour a, valid paths colour b etc) the input is recoloured as you type in response to validity for the specific tool you're about to invoke.
* There is no enforced standard for commands other than using a file name to invoke them.
* Different languages and frameworks have different and multiple ways of parsing command lines. For example Gooey (a python gui tool) works with scripts written with the argparse library but dodes not work with optparse.
* The terminal is not the shell. That means that to present a gui, you'll have to launch something that runs outside of the terminal to present the gui.
* It's common for developers to write command line tools with out understanding the shell and os's input and output system beyond reading and writing files. I routinely have to teach jr developers about stdio, stderr, pipes etc...
That said, there's great potential to take advantage of shell autocomplete files to make better guis for commands: https://blog.deepjyoti30.dev/tab-autocomplet-cli-apps . Someone probably already has done this...
Hmm. Writing a wrapper that uses autocomplete definitions might be more useful... There's also the approach of Zenity that gives you the ability to create GUIs from shell scripts. When you do have a gui from parser tool, it can be quite nice (like Python's gooey).
They will only use composition if there isn’t a tool that solves the problem by itself.
Which is actually also a problem with GUIs. Many times, with a few CLI commands you can do a ton of stuff that you just cannot represent in UI without having tons of buttons...