# Module proc_macro::tracked_env

source ·
🔬This is a nightly-only experimental API. (`proc_macro_tracked_env` #99515)
Expand description

Tracked access to environment variables.

## Functions

- var Experimental
  Retrieve an environment variable and add it to build dependency info. The build system executing the compiler will know that the variable was accessed during compilation, and will be able to rerun the build when the value of that variable changes. Besides the dependency tracking this function should be equivalent to `env::var` from the standard library, except that the argument must be UTF-8.