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Environment variables

Environment variables are a common way to configure various buildpacks at build-time.

Below are a few ways you can do so. All of them will use our samples repo for simplicity.

Using CLI arguments (--env)

The --env parameter must be one of the following:

  • VARIABLE=VALUE
  • VARIABLE, where the value of VARIABLE will be taken from the local environment
Example:
# clone the repo
git clone https://github.com/buildpacks/samples

# set an environment variable
export FOO=BAR

# build the app
pack build sample-app \
    --env "HELLO=WORLD" \
    --env "FOO" \
    --builder cnbs/sample-builder:bionic \
    --buildpack  samples/buildpacks/hello-world/ \
    --buildpack samples/apps/bash-script/bash-script-buildpack/ \
    --path  samples/apps/bash-script/

# run the app
docker run sample-app

The following environment variables were set and available to buildpacks at build-time:

Name Value Source
HELLO WORLD hard-coded inline value
FOO BAR current environment

Using env files (--env-file)

The --env-file parameter must be a path to a file where each line is one of the following:

  • VARIABLE=VALUE
  • VARIABLE, where the value of VARIABLE will be taken from the current environment
Example:
# clone the repo
git clone https://github.com/buildpacks/samples

# set an environment variable
export FOO=BAR

# create an env file
echo -en "HELLO=WORLD\nFOO" > ./envfile

# build the app
pack build sample-app \
    --env-file ./envfile \
    --builder cnbs/sample-builder:bionic \
    --buildpack  samples/buildpacks/hello-world/ \
    --buildpack samples/apps/bash-script/bash-script-buildpack/ \
    --path  samples/apps/bash-script/

# run the app
docker run sample-app

The following environment variables were set and available to buildpacks at build-time:

Name Value Source
HELLO WORLD hard-coded value in file
FOO BAR current environment

NOTE: Variables defined using --env take precedence over variables defined in --env-file.

Using Project Descriptor

The --descriptor parameter must be a path to a file which follows the project.toml schema. You can define environment variables in an env table in the file, and pass those into the application.

Example:
# clone the repo
git clone https://github.com/buildpacks/samples

# Add an environment variable to the project.toml
cat >> samples/apps/bash-script/project.toml <<EOL
[[build.env]]
name="HELLO"
value="WORLD"
EOL

# build the app
pack build sample-app \
    --builder cnbs/sample-builder:bionic \
    --buildpack  samples/buildpacks/hello-world/ \
    --buildpack samples/apps/bash-script/bash-script-buildpack/ \
    --path  samples/apps/bash-script/

# run the app
docker run sample-app

The following environment variables were set and available to buildpacks at build-time:

Name Value Source
HELLO WORLD hard-coded value in file

NOTE: Variables defined using --env or --env-file take precedence over variables defined in the project.toml.

NOTE: project.toml can’t detect environment variables (so, for instance, if one ran export FOO=BAR and added name=FOO to the project.toml, it wouldn’t detect any value set for FOO).

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