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hack/tools/prowjob-gen/README.md

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+# prowjob-gen
+
+Prowjob-gen is a tool which helps generating prowjob configuration.
+
+## Usage
+
+Flags:
+
+```txt
+  -config string
+        Path to the config file
+  -output-dir string
+        Path to the directory to create the files in
+  -templates-dir string
+        Path to the directory containing the template files referenced inside the config file
+```
+
+When running prowjob-gen, all flags need to be provided.
+The tool then will iterate over all templates defined in the config file and execute them per configured branch.
+
+The configuration file is supposed to be in yaml format and to be stored inside the [test-infra](github.com/kubernetes/test-infra)
+repository, we have to make sure it is not getting parsed as configuration for prow.
+Because of that the top-level key for the configuration file is `prow-ignored:`.
+
+A sample configuration looks as follows:
+
+```yaml
+prow_ignored:
+  branches:
+    main: # values below the branch here are available in the template 
+      kubekinsImage: "gcr.io/k8s-staging-test-infra/kubekins-e2e:v20231208-8b9fd88e88-1.29"
+      interval: "2h"
+      kubernetesVersionManagement: "v1.26.6@sha256:6e2d8b28a5b601defe327b98bd1c2d1930b49e5d8c512e1895099e4504007adb"
+      kubebuilderEnvtestKubernetesVersion: "1.26.1"
+      upgrades:
+      - from: "1.29"
+        to: "1.30"
+
+  templates:
+  - name: "cluster-api-periodics.yaml.tpl"
+    format: "cluster-api-periodics-%s.yaml"
+
+  versions:
+    "1.29":
+      etcd: "3.5.10-0"
+      coreDNS: "v1.11.1"
+      k8sRelease: "stable-1.29"
+    "1.30":
+      etcd: "3.5.10-0"
+      coreDNS: "v1.11.1"
+      k8sRelease: "ci/latest-1.30"
+```
+
+With this configuration, the template `cluster-api-periodics.yaml.tpl` would get executed for each branch.
+In this example we only configure the `main` branch which results in the output file `cluster-api-periodics-main.yaml`.
+
+When executing a template, the following functions are available as addition to the standard functions in go templates:
+
+- `TrimPrefix`: [strings.TrimPrefix](https://pkg.go.dev/strings#TrimPrefix)
+- `TrimSuffix`: [strings.TrimSuffix](https://pkg.go.dev/strings#TrimSuffix)
+- `ReplaceAll`: [strings.ReplaceAll](https://pkg.go.dev/strings#ReplaceAll)
+- `last`: `func(any) any`: returns the last element of an array or slice.
+
+When executing a template, the following variables are available:
+
+- `branch`: The branch name the file get's templated for (The key in `.prow_ignored.branches`).
+- `config`: The branch's configuration from `.prow_ignored.branches.<branch>`.
+- `versions`: The versions mapper from `.prow_ignored.versions`.