383 lines
15 KiB
Markdown
383 lines
15 KiB
Markdown
# Generating Bash Completions For Your Own cobra.Command
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If you are using the generator you can create a completion command by running
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```bash
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cobra add completion
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```
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Update the help text show how to install the bash_completion Linux show here [Kubectl docs show mac options](https://kubernetes.io/docs/tasks/tools/install-kubectl/#enabling-shell-autocompletion)
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Writing the shell script to stdout allows the most flexible use.
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```go
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// completionCmd represents the completion command
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var completionCmd = &cobra.Command{
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Use: "completion",
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Short: "Generates bash completion scripts",
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Long: `To load completion run
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. <(bitbucket completion)
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To configure your bash shell to load completions for each session add to your bashrc
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# ~/.bashrc or ~/.profile
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. <(bitbucket completion)
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`,
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Run: func(cmd *cobra.Command, args []string) {
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rootCmd.GenBashCompletion(os.Stdout);
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},
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}
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```
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**Note:** The cobra generator may include messages printed to stdout for example if the config file is loaded, this will break the auto complete script
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## Example from kubectl
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Generating bash completions from a cobra command is incredibly easy. An actual program which does so for the kubernetes kubectl binary is as follows:
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```go
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package main
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import (
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"io/ioutil"
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"os"
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"k8s.io/kubernetes/pkg/kubectl/cmd"
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"k8s.io/kubernetes/pkg/kubectl/cmd/util"
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)
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func main() {
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kubectl := cmd.NewKubectlCommand(util.NewFactory(nil), os.Stdin, ioutil.Discard, ioutil.Discard)
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kubectl.GenBashCompletionFile("out.sh")
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}
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```
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`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.
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## Have the completions code complete your 'nouns'
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### Static completion of nouns
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This method allows you to provide a pre-defined list of completion choices for your nouns using the `validArgs` field.
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For example, 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:
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```go
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validArgs []string = { "pod", "node", "service", "replicationcontroller" }
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cmd := &cobra.Command{
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Use: "get [(-o|--output=)json|yaml|template|...] (RESOURCE [NAME] | RESOURCE/NAME ...)",
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Short: "Display one or many resources",
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Long: get_long,
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Example: get_example,
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Run: func(cmd *cobra.Command, args []string) {
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err := RunGet(f, out, cmd, args)
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util.CheckErr(err)
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},
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ValidArgs: validArgs,
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}
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```
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Notice we put the "ValidArgs" on the "get" subcommand. Doing so will give results like
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```bash
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# kubectl get [tab][tab]
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node pod replicationcontroller service
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```
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### Plural form and shortcuts for nouns
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If your nouns have a number of aliases, you can define them alongside `ValidArgs` using `ArgAliases`:
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```go
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argAliases []string = { "pods", "nodes", "services", "svc", "replicationcontrollers", "rc" }
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cmd := &cobra.Command{
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...
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ValidArgs: validArgs,
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ArgAliases: argAliases
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}
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```
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The aliases are not shown to the user on tab completion, but they are accepted as valid nouns by
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the completion algorithm if entered manually, e.g. in:
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```bash
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# kubectl get rc [tab][tab]
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backend frontend database
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```
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Note that without declaring `rc` as an alias, the completion algorithm would show the list of nouns
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in this example again instead of the replication controllers.
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### Dynamic completion of nouns
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In some cases it is not possible to provide a list of possible completions in advance. Instead, the list of completions must be determined at execution-time. Cobra provides two ways of defining such dynamic completion of nouns. Note that both these methods can be used along-side each other as long as they are not both used for the same command.
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**Note**: *Custom Completions written in Go* will automatically work for other shell-completion scripts (e.g., Fish shell), while *Custom Completions written in Bash* will only work for Bash shell-completion. It is therefore recommended to use *Custom Completions written in Go*.
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#### 1. Custom completions of nouns written in Go
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In a similar fashion as for static completions, you can use the `ValidArgsFunction` field to provide a Go function that Cobra will execute when it needs the list of completion choices for the nouns of a command. Note that either `ValidArgs` or `ValidArgsFunction` can be used for a single cobra command, but not both.
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Simplified code from `helm status` looks like:
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```go
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cmd := &cobra.Command{
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Use: "status RELEASE_NAME",
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Short: "Display the status of the named release",
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Long: status_long,
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RunE: func(cmd *cobra.Command, args []string) {
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RunGet(args[0])
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},
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ValidArgsFunction: func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
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if len(args) != 0 {
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return nil, cobra.ShellCompDirectiveNoFileComp
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}
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return getReleasesFromCluster(toComplete), cobra.ShellCompDirectiveNoFileComp
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},
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}
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```
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Where `getReleasesFromCluster()` is a Go function that obtains the list of current Helm releases running on the Kubernetes cluster.
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Notice we put the `ValidArgsFunction` on the `status` subcommand. Let's assume the Helm releases on the cluster are: `harbor`, `notary`, `rook` and `thanos` then this dynamic completion will give results like
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```bash
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# helm status [tab][tab]
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harbor notary rook thanos
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```
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You may have noticed the use of `cobra.ShellCompDirective`. These directives are bit fields allowing to control some shell completion behaviors for your particular completion. You can combine them with the bit-or operator such as `cobra.ShellCompDirectiveNoSpace | cobra.ShellCompDirectiveNoFileComp`
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```go
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// Indicates an error occurred and completions should be ignored.
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ShellCompDirectiveError
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// Indicates that the shell should not add a space after the completion,
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// even if there is a single completion provided.
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ShellCompDirectiveNoSpace
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// Indicates that the shell should not provide file completion even when
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// no completion is provided.
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// This currently does not work for zsh or bash < 4
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ShellCompDirectiveNoFileComp
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// Indicates that the shell will perform its default behavior after completions
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// have been provided (this implies !ShellCompDirectiveNoSpace && !ShellCompDirectiveNoFileComp).
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ShellCompDirectiveDefault
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```
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When using the `ValidArgsFunction`, Cobra will call your registered function after having parsed all flags and arguments provided in the command-line. You therefore don't need to do this parsing yourself. For example, when a user calls `helm status --namespace my-rook-ns [tab][tab]`, Cobra will call your registered `ValidArgsFunction` after having parsed the `--namespace` flag, as it would have done when calling the `RunE` function.
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##### Debugging
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Cobra achieves dynamic completions written in Go through the use of a hidden command called by the completion script. To debug your Go completion code, you can call this hidden command directly:
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```bash
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# helm __complete status har<ENTER>
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harbor
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:4
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Completion ended with directive: ShellCompDirectiveNoFileComp # This is on stderr
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```
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***Important:*** If the noun to complete is empty, you must pass an empty parameter to the `__complete` command:
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```bash
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# helm __complete status ""<ENTER>
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harbor
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notary
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rook
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thanos
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:4
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Completion ended with directive: ShellCompDirectiveNoFileComp # This is on stderr
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```
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Calling the `__complete` command directly allows you to run the Go debugger to troubleshoot your code. You can also add printouts to your code; Cobra provides the following functions to use for printouts in Go completion code:
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```go
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// Prints to the completion script debug file (if BASH_COMP_DEBUG_FILE
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// is set to a file path) and optionally prints to stderr.
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cobra.CompDebug(msg string, printToStdErr bool) {
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cobra.CompDebugln(msg string, printToStdErr bool)
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// Prints to the completion script debug file (if BASH_COMP_DEBUG_FILE
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// is set to a file path) and to stderr.
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cobra.CompError(msg string)
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cobra.CompErrorln(msg string)
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```
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***Important:*** You should **not** leave traces that print to stdout in your completion code as they will be interpreted as completion choices by the completion script. Instead, use the cobra-provided debugging traces functions mentioned above.
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#### 2. Custom completions of nouns written in Bash
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This method allows you to inject bash functions into the completion script. Those bash functions are responsible for providing the completion choices for your own completions.
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Some more actual code that works in kubernetes:
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```bash
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const (
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bash_completion_func = `__kubectl_parse_get()
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{
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local kubectl_output out
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if kubectl_output=$(kubectl get --no-headers "$1" 2>/dev/null); then
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out=($(echo "${kubectl_output}" | awk '{print $1}'))
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COMPREPLY=( $( compgen -W "${out[*]}" -- "$cur" ) )
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fi
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}
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__kubectl_get_resource()
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{
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if [[ ${#nouns[@]} -eq 0 ]]; then
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return 1
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fi
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__kubectl_parse_get ${nouns[${#nouns[@]} -1]}
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if [[ $? -eq 0 ]]; then
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return 0
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fi
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}
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__kubectl_custom_func() {
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case ${last_command} in
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kubectl_get | kubectl_describe | kubectl_delete | kubectl_stop)
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__kubectl_get_resource
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return
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;;
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*)
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;;
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esac
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}
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`)
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```
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And then I set that in my command definition:
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```go
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cmds := &cobra.Command{
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Use: "kubectl",
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Short: "kubectl controls the Kubernetes cluster manager",
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Long: `kubectl controls the Kubernetes cluster manager.
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Find more information at https://github.com/GoogleCloudPlatform/kubernetes.`,
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Run: runHelp,
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BashCompletionFunction: bash_completion_func,
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}
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```
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The `BashCompletionFunction` option is really only valid/useful on the root command. Doing the above will cause `__kubectl_custom_func()` (`__<command-use>_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 `__kubectl_customc_func()` will run because the cobra.Command only understood "kubectl" and "get." `__kubectl_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 then set `COMPREPLY` to valid pods!
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## Mark flags as required
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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.
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```go
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cmd.MarkFlagRequired("pod")
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cmd.MarkFlagRequired("container")
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```
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and you'll get something like
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```bash
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# kubectl exec [tab][tab][tab]
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-c --container= -p --pod=
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```
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# Specify valid filename extensions for flags that take a filename
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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.
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```go
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annotations := []string{"json", "yaml", "yml"}
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annotation := make(map[string][]string)
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annotation[cobra.BashCompFilenameExt] = annotations
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flag := &pflag.Flag{
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Name: "filename",
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Shorthand: "f",
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Usage: usage,
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Value: value,
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DefValue: value.String(),
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Annotations: annotation,
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}
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cmd.Flags().AddFlag(flag)
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```
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Now when you run a command with this filename flag you'll get something like
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```bash
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# kubectl create -f
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test/ example/ rpmbuild/
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hello.yml test.json
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```
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So while there are many other files in the CWD it only shows me subdirs and those with valid extensions.
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# Specify custom flag completion
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As for nouns, Cobra provides two ways of defining dynamic completion of flags. Note that both these methods can be used along-side each other as long as they are not both used for the same flag.
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**Note**: *Custom Completions written in Go* will automatically work for other shell-completion scripts (e.g., Fish shell), while *Custom Completions written in Bash* will only work for Bash shell-completion. It is therefore recommended to use *Custom Completions written in Go*.
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## 1. Custom completions of flags written in Go
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To provide a Go function that Cobra will execute when it needs the list of completion choices for a flag, you must register the function in the following manner:
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```go
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flagName := "output"
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cmd.RegisterFlagCompletionFunc(flagName, func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
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return []string{"json", "table", "yaml"}, cobra.ShellCompDirectiveDefault
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})
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```
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Notice that calling `RegisterFlagCompletionFunc()` is done through the `command` with which the flag is associated. In our example this dynamic completion will give results like so:
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```bash
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# helm status --output [tab][tab]
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json table yaml
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```
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### Debugging
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You can also easily debug your Go completion code for flags:
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```bash
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# helm __complete status --output ""
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json
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table
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yaml
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:4
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Completion ended with directive: ShellCompDirectiveNoFileComp # This is on stderr
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```
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***Important:*** You should **not** leave traces that print to stdout in your completion code as they will be interpreted as completion choices by the completion script. Instead, use the cobra-provided debugging traces functions mentioned in the above section.
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## 2. Custom completions of flags written in Bash
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Alternatively, you can use bash code for flag custom completion. Similar to the filename
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completion and filtering using `cobra.BashCompFilenameExt`, you can specify
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a custom flag completion bash function with `cobra.BashCompCustom`:
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```go
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annotation := make(map[string][]string)
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annotation[cobra.BashCompCustom] = []string{"__kubectl_get_namespaces"}
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flag := &pflag.Flag{
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Name: "namespace",
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Usage: usage,
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Annotations: annotation,
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}
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cmd.Flags().AddFlag(flag)
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```
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In addition add the `__kubectl_get_namespaces` implementation in the `BashCompletionFunction`
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value, e.g.:
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```bash
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__kubectl_get_namespaces()
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{
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local template
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template="{{ range .items }}{{ .metadata.name }} {{ end }}"
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local kubectl_out
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if kubectl_out=$(kubectl get -o template --template="${template}" namespace 2>/dev/null); then
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COMPREPLY=( $( compgen -W "${kubectl_out}[*]" -- "$cur" ) )
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fi
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}
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```
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# Using bash aliases for commands
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You can also configure the `bash aliases` for the commands and they will also support completions.
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```bash
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alias aliasname=origcommand
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complete -o default -F __start_origcommand aliasname
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# and now when you run `aliasname` completion will make
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# suggestions as it did for `origcommand`.
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$) aliasname <tab><tab>
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completion firstcommand secondcommand
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```
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