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
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.
Note that Cargo will also read environment variables for
configuration values, as described in that documentation
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:
let version = env!("CARGO_PKG_VERSION");
version will now contain the value of
CARGO- Path to the
cargobinary 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 of your package.
CARGO_PKG_HOMEPAGE- The home page 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:
use std::env; let out_dir = env::var("OUT_DIR").unwrap();
out_dir will now contain the value of
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
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
CARGO_CFG_<cfg>- For each configuration option 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
_. 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. Some more information about target triples can be found in clang’s own documentation.
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
-jparameter 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 -jas 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.
DEBUG- values of the corresponding variables for the profile currently being built.
releasefor release builds,
debugfor other builds.
DEP_<name>_<key>- For more information about this set of environment variables, see build script documentation about
RUSTDOC- the compiler and documentation generator that Cargo has resolved to use, passed to the build script so it might use it as well.
Environment variables Cargo sets for 3rd party subcommands
Cargo exposes this environment variable to 3rd party subcommands
(ie. programs named
cargo-foobar placed in
CARGO- Path to the
cargobinary performing the build.