Conditionals

tip

We recommend reviewing Go Templates documentation before attempting to create a template.

If you're new to YAML we also recommend reviewing the YAML 1.2 spec for validation on syntax.

Overview

From Go template Conditional:

{{if pipeline}}
  T1
{{end}}

If the value of the pipeline is empty, no output is generated; otherwise, T1 is executed. The empty values are false, 0, any nil pointer or interface value, and any array, slice, map, or string of length zero. Dot is unaffected.

tip

For information on if/else statements see conditional docs

Sample

Let's take a look at using a conditional with a variable in a template:

metadata:
  template: true

{{$br := vela "BUILD_BRANCH"}}

steps:

  - name: test
    commands:
      - go test ./...
    image: {{ .image }}
    {{ .pull_policy }}
    ruleset:
      event: [ push, pull_request ]

  # if branch equals main add this step to the final pipeline
  {{ if (eq $br "main") }}

  - name: build
    commands:
      - go build
    image: {{ .image }}
    {{ .pull_policy }}
    ruleset:
      event: [ push, pull_request ]

  {{ end }}

The caller of this template could look like:

version: "1"
templates:
  - name: sample
    source: github.com/<org>/<repo>/path/to/file/<template>.yml
    type: github

steps:
  - name: golang
    template:
      name: sample
      vars:
        image: golang:latest
        pull_policy: "pull: always"

Which means the compiled pipeline for execution on a worker is:

version: "1"
steps:
  - name: sample_test
    commands:
      - go test ./...
    image: golang:latest
    pull: always
    ruleset:
      event: [ push, pull_request ]

  - name: sample_build
    commands:
      - go build
    image: golang:latest
    pull: always
    ruleset:
      event: [ push, pull_request ]