“Clearing” the buildpack environment with clear-env is the process of preventing end-users from customizing a buildpack’s behavior through environment variables.

Buildpack authors may elect to clear user-provided environment variables when bin/detect and bin/build are executed. This is achieved by setting clear-env to true in buildpack.toml; by default clear-env is set to false.

• When clear-env is set to true for a given buildpack, the lifecycle will not set user-provided environment variables when running /bin/detect or /bin/build.
• If a buildpack does allow customization by the end-user through the environment (clear-env is false), there is a special convention for naming the environment variables recognized by the buildpack, shown in the following table:

Env Variable	Description	Detect	Build	Launch
BP_*	User-provided variable for buildpack	[x]	[x]
BPL_*	User-provided variable for exec.d			[x]

Further Reading

For more about how environment variables are specified by end-users, see the page for how to customize buildpack behavior with build-time environment variables.

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