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This input type executes an external script or binary. This can be used to manipulate already compiled files or execute binaries outside of kapitan that generate or manipulate files.

For example, ytt is a useful yaml templating tool. It is not built into the kapitan binary, however, with the external input type, we could specify the ytt binary to be executed with specific arguments and environment variables.

In this example, we're removing a label from a k8s manifests in a directory ingresses and placing it into the compiled target directory.

  target_name: k8s-manifests
      target: ${target_name}
      - input_type: external
          - /usr/local/bin/ytt # path to ytt on system
        output_path: .
          - -f
          - ingresses/ # directory with ingresses
          - -f
          - ytt/remove.yaml # custom ytt script
          - ">"
          - \${compiled_target_dir}/ingresses/ingresses.yaml # final merged result

Supported output types: N/A (no need to specify output_type)

Additionally, the input type supports field env_vars, which can be used to set environment variables for the external command. By default, the external command doesn't inherit any environment variables from Kapitan's environment. However, if environment variables $PATH or $HOME aren't set in env_vars, they will be propagated from Kapitan's environment to the external command's environment.

Finally, Kapitan will substitute ${compiled_target_dir} in both the command's arguments and the environment variables. This variable needs to be escaped in the configuration to ensure that reclass won't interpret it as a reclass reference.