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Introduction

Pipeline chaining refers to the process of linking multiple pipelines together, where the output of one pipeline becomes the input of another. This allows for the sequential execution of processing steps, creating a complex workflow. By automating this chain, you can ensure proper testing and deployment of applications, enhancing the overall efficiency and reliability of the process.

More details on this here: https://developer.harness.io/docs/platform/pipelines/pipeline-chaining/

Problem statement​

How to get output variables from the previous stage in a chained pipeline from another stage.

Steps to achieve this usecase​

At the parent pipeline level in the output section, the User can provide the expression of the output variable for the chained pipeline.

In the below-shared pipeline yaml the first stage is the pipeline stage, In the output section We have defined the expression of the child pipeline which we want to use in the parent pipeline.

The same variable defined in the output section can be used by the further stage with the expression - <+pipeline.[pipeline_stage_identifier].[output_variable_defined_under_output_section]>.

pipeline:
  name: parentPipelineDemo
  identifier: parentPipelineDemo
  projectIdentifier: naidusanity
  orgIdentifier: default
  tags: {}
  stages:
    - stage:
        name: stage1
        identifier: stage1
        description: ""
        type: Pipeline
        spec:
          org: default
          pipeline: childPipelineDemo
          project: naidusanity
          outputs:
            - name: parentOutput
      value: <+pipeline.stages.custom.spec.execution.steps.ShellScript_1.output.outputVariables.outputVar>
    - stage:
        name: cusom2
        identifier: cusom2
        description: ""
        type: Custom
        spec:
          execution:
            steps:
              - step:
                  type: ShellScript
                  name: ShellScript_1
                  identifier: ShellScript_1
                  spec:
                    shell: Bash
                    onDelegate: true
                    source:
                      type: Inline
                      spec:
                        script: |-
                          echo "Printing child values using parent output"
                          echo <+pipeline.stages.stage1.output.parentOutput>
                    environmentVariables: []
                    outputVariables: []
                  timeout: 10m
        tags: {}

This is how you can use an output variable from a previous stage in a chained pipeline from another stage.