## Environment Variables

Cargo sets and reads a number of environment variables which your code can detect
or override. Here is a list of the variables Cargo sets, organized by when it interacts
with them:

### Environment variables Cargo reads

You can override these environment variables to change Cargo's behavior on your
system:

* `CARGO_HOME` — Cargo maintains a local cache of the registry index and of git
  checkouts of crates. By default these are stored under `$HOME/.cargo`, but
  this variable overrides the location of this directory. Once a crate is cached
  it is not removed by the clean command.
* `CARGO_TARGET_DIR` — Location of where to place all generated artifacts,
  relative to the current working directory.
* `RUSTC` — Instead of running `rustc`, Cargo will execute this specified
  compiler instead.
* `RUSTC_WRAPPER` — Instead of simply running `rustc`, Cargo will execute this
  specified wrapper instead, passing as its commandline arguments the rustc
  invocation, with the first argument being rustc.
* `RUSTDOC` — Instead of running `rustdoc`, Cargo will execute this specified
  `rustdoc` instance instead.
* `RUSTDOCFLAGS` — A space-separated list of custom flags to pass to all `rustdoc`
  invocations that Cargo performs. In contrast with `cargo rustdoc`, this is
  useful for passing a flag to *all* `rustdoc` instances.
* `RUSTFLAGS` — A space-separated list of custom flags to pass to all compiler
  invocations that Cargo performs. In contrast with `cargo rustc`, this is
  useful for passing a flag to *all* compiler instances.
* `CARGO_INCREMENTAL` — If this is set to 1 then Cargo will force incremental
  compilation to be enabled for the current compilation, and when set to 0 it
  will force disabling it. If this env var isn't present then cargo's defaults
  will otherwise be used.
* `CARGO_CACHE_RUSTC_INFO` — If this is set to 0 then Cargo will not try to cache
  compiler version information.

Note that Cargo will also read environment variables for `.cargo/config`
configuration values, as described in [that documentation][config-env]

[config-env]: reference/config.html#environment-variables

### Environment variables Cargo sets for crates

Cargo exposes these environment variables to your crate when it is compiled.
Note that this applies for test binaries as well.
To get the value of any of these variables in a Rust program, do this:

```rust
let version = env!("CARGO_PKG_VERSION");
```

`version` will now contain the value of `CARGO_PKG_VERSION`.

* `CARGO` - Path to the `cargo` binary performing the build.
* `CARGO_MANIFEST_DIR` - The directory containing the manifest of your package.
* `CARGO_PKG_VERSION` - The full version of your package.
* `CARGO_PKG_VERSION_MAJOR` - The major version of your package.
* `CARGO_PKG_VERSION_MINOR` - The minor version of your package.
* `CARGO_PKG_VERSION_PATCH` - The patch version of your package.
* `CARGO_PKG_VERSION_PRE` - The pre-release version of your package.
* `CARGO_PKG_AUTHORS` - Colon separated list of authors from the manifest of your package.
* `CARGO_PKG_NAME` - The name of your package.
* `CARGO_PKG_DESCRIPTION` - The description from the manifest of your package.
* `CARGO_PKG_HOMEPAGE` - The home page from the manifest of your package.
* `CARGO_PKG_REPOSITORY` - The repository from the manifest of your package.
* `OUT_DIR` - If the package has a build script, this is set to the folder where the build
              script should place its output. See below for more information.

### Environment variables Cargo sets for build scripts

Cargo sets several environment variables when build scripts are run. Because these variables
are not yet set when the build script is compiled, the above example using `env!` won't work
and instead you'll need to retrieve the values when the build script is run:

```rust
use std::env;
let out_dir = env::var("OUT_DIR").unwrap();
```

`out_dir` will now contain the value of `OUT_DIR`.

* `CARGO` - Path to the `cargo` binary performing the build.
* `CARGO_MANIFEST_DIR` - The directory containing the manifest for the package
                         being built (the package containing the build
                         script). Also note that this is the value of the
                         current working directory of the build script when it
                         starts.
* `CARGO_MANIFEST_LINKS` - the manifest `links` value.
* `CARGO_FEATURE_<name>` - For each activated feature of the package being
                           built, this environment variable will be present
                           where `<name>` is the name of the feature uppercased
                           and having `-` translated to `_`.
* `CARGO_CFG_<cfg>` - For each [configuration option][configuration] of the
                      package being built, this environment variable will
                      contain the value of the configuration, where `<cfg>` is
                      the name of the configuration uppercased and having `-`
                      translated to `_`.
                      Boolean configurations are present if they are set, and
                      not present otherwise.
                      Configurations with multiple values are joined to a
                      single variable with the values delimited by `,`.
* `OUT_DIR` - the folder in which all output should be placed. This folder is
              inside the build directory for the package being built, and it is
              unique for the package in question.
* `TARGET` - the target triple that is being compiled for. Native code should be
             compiled for this triple. See the [Target Triple] description
             for more information.
* `HOST` - the host triple of the rust compiler.
* `NUM_JOBS` - the parallelism specified as the top-level parallelism. This can
               be useful to pass a `-j` parameter to a system like `make`. Note
               that care should be taken when interpreting this environment
               variable. For historical purposes this is still provided but
               recent versions of Cargo, for example, do not need to run `make
               -j` as it'll automatically happen. Cargo implements its own
               [jobserver] and will allow build scripts to inherit this
               information, so programs compatible with GNU make jobservers will
               already have appropriately configured parallelism.
* `OPT_LEVEL`, `DEBUG` - values of the corresponding variables for the
                         profile currently being built.
* `PROFILE` - `release` for release builds, `debug` for other builds.
* `DEP_<name>_<key>` - For more information about this set of environment
                       variables, see build script documentation about [`links`][links].
* `RUSTC`, `RUSTDOC` - the compiler and documentation generator that Cargo has
                       resolved to use, passed to the build script so it might
                       use it as well.
* `RUSTC_LINKER` - The path to the linker binary that Cargo has resolved to use
                   for the current target, if specified. The linker can be
                   changed by editing `.cargo/config`; see the documentation
                   about [cargo configuration][cargo-config] for more
                   information.

[links]: reference/build-scripts.html#the-links-manifest-key
[configuration]: https://doc.rust-lang.org/reference/attributes.html#conditional-compilation
[jobserver]: https://www.gnu.org/software/make/manual/html_node/Job-Slots.html
[cargo-config]: reference/config.html
[Target Triple]: appendix/glossary.html#target

### Environment variables Cargo sets for 3rd party subcommands

Cargo exposes this environment variable to 3rd party subcommands
(ie. programs named `cargo-foobar` placed in `$PATH`):

* `CARGO` - Path to the `cargo` binary performing the build.
