`out.sh` will get you completions of subcommands and flags. Copy it to `/etc/bash_completion.d/` as described [here](https://debian-administration.org/article/316/An_introduction_to_bash_completion_part_1) and reset your terminal to use autocompletion. If you make additional annotations to your code, you can get even more intelligent and flexible behavior.
Short: "kubectl controls the Kubernetes cluster manager",
Long: `kubectl controls the Kubernetes cluster manager.
Find more information at https://github.com/GoogleCloudPlatform/kubernetes.`,
Run: runHelp,
BashCompletionFunction: bash_completion_func,
}
```
The `BashCompletionFunction` option is really only valid/useful on the root command. Doing the above will cause `__custom_func()` to be called when the built in processor was unable to find a solution. In the case of kubernetes a valid command might look something like `kubectl get pod [mypod]`. If you type`kubectl get pod [tab][tab]` the `__customc_func()` will run because the cobra.Command only understood "kubectl" and "get."`__custom_func()` will see that the cobra.Command is "kubectl_get" and will thus call another helper `__kubectl_get_resource()`. `__kubectl_get_resource` will look at the 'nouns' collected. In our example the only noun will be `pod`. So it will call `__kubectl_parse_get pod`. `__kubectl_parse_get` will actually call out to kubernetes and get any pods. It will thenset`COMPREPLY` to valid pods!
## Have the completions code complete your 'nouns'
In the above example "pod" was assumed to already be typed. But if you want `kubectl get [tab][tab]` to show a list of valid "nouns" you have to set them. Simplified code from `kubectl get` looks like:
Most of the time completions will only show subcommands. But if a flag is required to make a subcommand work, you probably want it to show up when the user types [tab][tab]. Marking a flag as 'Required' is incredibly easy.
```go
cmd.MarkFlagRequired("pod")
cmd.MarkFlagRequired("container")
```
and you'll get something like
```bash
# kubectl exec [tab][tab][tab]
-c --container= -p --pod=
```
# Specify valid filename extensions for flags that take a filename
In this example we use --filename= and expect to get a json or yaml file as the argument. To make this easier we annotate the --filename flag with valid filename extensions.