# Library quick start

> Add grit-lib to a Rust project, open a repository, and read the current commit from HEAD.

This page walks through a minimal program that discovers a Git repository in the current directory (or a parent), resolves `HEAD`, and prints the commit id and subject line. The source below is the real example binary in the Grit repository; it is included automatically so the docs cannot drift from compiled code.

## Add the dependency

In your crate:

```bash
cargo add grit-lib
```

Or add to `Cargo.toml`:

```toml
[dependencies]
grit-lib = "0.5.0"
```

Use the [latest version on crates.io](https://crates.io/crates/grit-lib) if the number above is stale.

## Example program

Save as `src/main.rs` (or copy from `grit-examples` in the Grit repo):

```rust
//! Minimal grit-lib program: discover a repository and print HEAD's commit id.
//!
//! Source for the library quick start in the docs; kept in sync via an include directive.

use grit_lib::objects::{parse_commit, ObjectKind};
use grit_lib::repo::Repository;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let repo = Repository::discover(None)?;
    let head = grit_lib::refs::resolve_ref(&repo.git_dir, "HEAD")?;
    let object = repo.odb.read(&head)?;
    if object.kind != ObjectKind::Commit {
        return Err("HEAD is not a commit".into());
    }
    let commit = parse_commit(&object.data)?;
    println!("{head}");
    let subject = commit.message.lines().next().unwrap_or("");
    if !subject.is_empty() {
        println!("{subject}");
    }
    Ok(())
}
```

## Run it

From the root of any Git repository with at least one commit:

```bash
cargo run
```

Example output (your commit id will differ):

```text
217c6f9a1b2c3d4e5f6789012345678901234567
Start the project
```

The first line is the full object id of `HEAD`; the second is the first line of the commit message.

## Next steps

- [Library guide overview](https://grit-scm.com/docs/library/index.md) — longer-form guides for objects, refs, diff, and network code.
- [grit-lib on docs.rs](https://docs.rs/grit-lib) — API reference for `Repository` and the rest of the public surface.
- [Tutorial](https://grit-scm.com/docs/tutorial/index.md) — the same repository operations from the `grit` CLI.