With the TektonCD CLI we have a system of “plugins”, it’s the same very simple CLI plugin system you have with git or kubectl, if you do a :
kubectl blah foo --bar
since kubectl knows it doesn’t have the blah command will try to go over the
filesystem paths in your $PATH environment and sees if there is a binary
called kubectl-blah and if it finds it will pass the arguments to the binary
which effectively become :
kubectl-blah foo --bar
all very transparent and easy to install and use.
The problem with this is that the user doesn’t really knows about it and discovery is limited unless the user knows about the command already.
kubectl added a plugin list argument to list easily all plugins available (or in kubectl case you can just use krew to manage kubectl plugins).
For tektoncd-cli we wanted to shows it directly in the Root commands help. So when the user type tkn help it will shows the plugin list.
Since tektoncd-cli is using the spf13/cobra library, and the lib being very extensible, it wasn’t hard to extend the help system.
You first need to define a custom “usage template”, the template we have is this one :
https://github.com/chmouel/tektoncd-cli/blob/add-available-plugins-from-path/pkg/cmd/root.go#L46
It adds this snippet to the default template :
{{if gt (len pluginList) 0}}
Available Plugins:
{{- range pluginList}}
{{.}}{{end}}{{end}}{{if .HasAvailableLocalFlags}}
The pluginList template variable is a slice of plugins which is discovered in this function :
func addPluginsToHelp() {
pluginlist := []string{}
paths := strings.Split(os.Getenv("PATH"), ":")
// go over all paths in the PATH environment
// and add them to the completion command
for _, path := range paths {
// list all files in path
files, err := ioutil.ReadDir(path)
if err != nil {
continue
}
// add all files that start with tkn-
for _, file := range files {
if strings.HasPrefix(file.Name(), "tkn-") {
basep := strings.ReplaceAll(file.Name(), "tkn-", "")
fpath := filepath.Join(path, file.Name())
info, err := os.Stat(fpath)
if err != nil {
continue
}
if info.Mode()&0o111 != 0 {
pluginlist = append(pluginlist, basep)
}
}
}
}
cobra.AddTemplateFunc("pluginList", func() []string { return pluginlist })
}
what it does is, go over the environement variable PATH gets all directories from there, check all executable binaries that starts with the “tkn-” prefix and add it to the template variable pluginList inside a slice of strings.
The plugin command will show then nicely when doing tkn help. for example with the Pipelines as Code CLI installed, I will get this :
$ tkn help
CLI for tekton pipelines
Usage:
tkn [flags]
tkn [command]
Available Commands:
bundle Manage Tekton Bundles
chain Manage Chains
clustertask Manage ClusterTasks
condition Manage Conditions
eventlistener Manage EventListeners
hub Interact with tekton hub
pipeline Manage pipelines
pipelinerun Manage PipelineRuns
resource Manage pipeline resources
task Manage Tasks
taskrun Manage TaskRuns
triggerbinding Manage TriggerBindings
triggertemplate Manage TriggerTemplates
Other Commands:
completion Prints shell completion scripts
version Prints version information
Available Plugins:
pac
Flags:
-h, --help help for tkn
Use "tkn [command] --help" for more information about a command.
There is maybe area for improvement to be able to get a small snippet of what the plugin is actually doing in the future but so far having it in the root help is a great boost for CLI discoverability.
The full PR on tektoncd cli is here if you wanted to look at the full code and tests :