Hello fellow rustaceans! Recently, there was a thread about how we can grow this community (how can I link to posts across servers?), where I already talked briefly about this topic, saying that I did not know if it is worthy of a full post here, as most things seem to be pretty professional looking links to talks and blogs. I've gotten some encouragement to post it, so here we go:

When to use a library instead of a CLI

I'm working on a little project called Autcrate in my free time, which aims to streamline the release and publishing process (what exactly it does isn't really important for this discussion). Autocrate uses git to get the path of the current repo, tags and pushes releases, generates a change log from commits and so on.

Up until a week ago, I was just using the git2 library crate, which offers the functionalities of libgit2 for rust. While good, using this crate is much more complicated than for example just executing git push from my program using std::process::command. I am only using the porcelain functionalities of git (as of now), so all functionality could be achieved by calling the CLI interface.

Question

When is it acceptable to use CLI Commands instead of using libraries provided for that same software?

Is it generally better to use API/ABI from libraries, or is it maybe even better to use the CLI interface, reducing the list of dependencies?

Pro and Con of using Commands instead of libraries

Pro	Con
Reduces the dependencies of a crate	Adds a dependency that cannot be tracked by cargo
Much easier to program for developers	The CLI interface is not versioned and might break in the future
Documentation of the CLI interface is often better than of libraries	Bad usage of command cannot be detected at compile time
Cli program might not be available depending on architecture or platform

(this is of course not an exhaustive list. I will edit it if something comes up in the thread.)

Edit

Alright then. Thank you for your answers. While using the git CLI would probably be fine, since it's very stable and available on most systems (especially those for CI/CD), it might change and is at best hacky. I'll be doing the "right" thing and use libgit2 instead of just calling CLI commands.

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[–] sugar_in_your_tea@sh.itjust.works 9 points 8 months ago

Here are some other reasons:

users can install any version of a CLI command, so you could get weird breakage, whereas you control the version with a cargo dependency
CLI commands can have variability with user configuration, whereas libraries typically don't

But each of those can also be a benefit:

you probably don't need to patch your software if a security vulnerability lies in the CLI command, the user can just patch their system
users being able to customize the CLI may make your app easier to write (i.e. you don't need to reproduce those same configuration options)

So it really depends on your target use case. But in general, a library is probably better for code you intend to share with others or put in production.