Being able to modify the runtime environment variables from the scripts inside an appimage-builder recipe has been an old feature request in our backlog. This would us to move the whole build process of the binaries inside the recipe and extract information from it to use it later.

This feature is available in development version (master branch) and will be released in appimage-builder v0.8.4.

Usage

• Export the variables to a special file located at $BUILD_ENV.
• Use the variable in your recipe using double curly brackets: {{VAR_NAME}}

script:
 - echo "MY_VAR=VALUE" >> $BUILDER_ENV
 
AppDIR:
  name: my-app {{BUILDER_ENV}}

Limitations

Exported variables will be available once the script section is completed. Therefore, you will need to use the export command in order to make a variable reachable inside the current script as follows:

script:
 - echo "MY_VAR=VALUE" >> $BUILDER_ENV
 - export MY_VAR=VALUE

Old style env variables declared using !ENV and ${VAR_NAME} are evaluated before running the script section and will not work in this scenario. Use double curly brackets instead.

How it works ?

The implementation was inspired by the Github Actions way of dealing with environment variables and works as follows.

For each script section appimage-builder creates a temporary file and exports its path using the BUILDER_ENV variable. This file can be modified from the script using an echo command or something alike. Once the script execution is completed, the entries in the file are appended to the process environment.

The double curly bracket notation is used to resolve environment variables. Unlike the old notation, these variables are evaluated only when they are required and can be undefined at the start of appimage-builder

Conclusions

Now you can set environment variables from the script sections and use them later on appimage-builder. This feature can be used to get some metadata from your application and use it later.

I wonder which other uses it may have? Any ideas, leave a comment.