**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 so must be removed.
# Customizing completions
The generated completion scripts will automatically handle completing commands and flags. However, you can make your completions much more powerful by providing information to complete your program's nouns and flag values.
## Completion of nouns
### Static completion of nouns
Cobra allows you to provide a pre-defined list of completion choices for your nouns using the `ValidArgs` field.
For example, if you want `kubectl get [tab][tab]` to show a list of valid "nouns" you have to set them.
Some simplified code from `kubectl get` looks like:
The aliases are not shown to the user on tab completion, but they are accepted as valid nouns by
the completion algorithm if entered manually, e.g. in:
```bash
$ kubectl get rc [tab][tab]
backend frontend database
```
Note that without declaring `rc` as an alias, the completion algorithm would not know to show the list of
replication controllers following `rc`.
### Dynamic completion of nouns
In some cases it is not possible to provide a list of completions in advance. Instead, the list of completions must be determined at execution-time. 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.
Where `getReleasesFromCluster()` is a Go function that obtains the list of current Helm releases running on the Kubernetes cluster.
Notice we put the `ValidArgsFunction` on the `status` sub-command. Let's assume the Helm releases on the cluster are: `harbor`, `notary`, `rook` and `thanos` then this dynamic completion will give results like:
```bash
$ helm status [tab][tab]
harbor notary rook thanos
```
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`
```go
// Indicates that the shell will perform its default behavior after completions
// have been provided (this implies none of the other directives).
ShellCompDirectiveDefault
// Indicates an error occurred and completions should be ignored.
ShellCompDirectiveError
// Indicates that the shell should not add a space after the completion,
// even if there is a single completion provided.
ShellCompDirectiveNoSpace
// Indicates that the shell should not provide file completion even when
// no completion is provided.
ShellCompDirectiveNoFileComp
// Indicates that the returned completions should be used as file extension filters.
// For example, to complete only files of the form *.json or *.yaml:
***Note***: 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.
#### Debugging
Cobra achieves dynamic completion 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:
```bash
$ helm __complete status har<ENTER>
harbor
:4
Completion ended with directive: ShellCompDirectiveNoFileComp # This is on stderr
```
***Important:*** If the noun to complete is empty (when the user has not yet typed any letters of that noun), you must pass an empty parameter to the `__complete` command:
```bash
$ helm __complete status ""<ENTER>
harbor
notary
rook
thanos
:4
Completion ended with directive: ShellCompDirectiveNoFileComp # This is on stderr
```
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:
```go
// Prints to the completion script debug file (if BASH_COMP_DEBUG_FILE
// is set to a file path) and optionally prints to stderr.
cobra.CompDebug(msg string, printToStdErr bool) {
cobra.CompDebugln(msg string, printToStdErr bool)
// Prints to the completion script debug file (if BASH_COMP_DEBUG_FILE
// is set to a file path) and to stderr.
cobra.CompError(msg string)
cobra.CompErrorln(msg string)
```
***Important:*** You should **not** leave traces that print directly 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.
## Completions for flags
### Mark flags as required
Most of the time completions will only show sub-commands. But if a flag is required to make a sub-command work, you probably want it to show up when the user types [tab][tab]. You can mark a flag as 'Required' like so:
```go
cmd.MarkFlagRequired("pod")
cmd.MarkFlagRequired("container")
```
and you'll get something like
```bash
$ kubectl exec [tab][tab]
-c --container= -p --pod=
```
### Specify dynamic flag completion
As for nouns, Cobra provides a way of defining dynamic completion of flags. 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 using the `command.RegisterFlagCompletionFunc()` function.
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:
```bash
$ helm status --output [tab][tab]
json table yaml
```
#### Debugging
You can also easily debug your Go completion code for flags:
```bash
$ helm __complete status --output ""
json
table
yaml
:4
Completion ended with directive: ShellCompDirectiveNoFileComp # This is on stderr
```
***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 further above.
### Specify valid filename extensions for flags that take a filename
To limit completions of flag values to file names with certain extensions you can either use the different `MarkFlagFilename()` functions or a combination of `RegisterFlagCompletionFunc()` and `ShellCompDirectiveFilterFileExt`, like so:
To limit completions of flag values to directory names you can either use the `MarkFlagDirname()` functions or a combination of `RegisterFlagCompletionFunc()` and `ShellCompDirectiveFilterDirs`, like so:
To limit completions of flag values to directory names *within another directory* you can use a combination of `RegisterFlagCompletionFunc()` and `ShellCompDirectiveFilterDirs` like so:
Both `zsh` and `fish` allow for descriptions to annotate completion choices. For commands and flags, Cobra will provide the descriptions automatically, based on usage information. For example, using zsh:
```
$ helm s[tab]
search -- search for a keyword in charts
show -- show information of a chart
status -- displays the status of the named release
```
while using fish:
```
$ helm s[tab]
search (search for a keyword in charts) show (show information of a chart) status (displays the status of the named release)
```
Cobra allows you to add annotations to your own completions. Simply add the annotation text after each completion, following a `\t` separator. This technique applies to completions returned by `ValidArgs`, `ValidArgsFunction` and `RegisterFlagCompletionFunc()`. For example:
ValidArgs: []string{"bash\tCompletions for bash", "zsh\tCompletions for zsh"}
```
## Bash completions
### Dependencies
The bash completion script generated by Cobra requires the `bash_completion` package. You should update the help text of your completion command to show how to install the `bash_completion` package ([Kubectl docs](https://kubernetes.io/docs/tasks/tools/install-kubectl/#enabling-shell-autocompletion))
### Aliases
You can also configure `bash` aliases for your program and they will also support completions.
Zsh supports descriptions for completions. Cobra will provide the description automatically,
based on usage information. Cobra provides a way to completely disable such descriptions by
using `GenZshCompletionNoDesc()` or `GenZshCompletionFileNoDesc()`. You can choose to make
this a configurable option to your users.
```
# With descriptions
$ helm s[tab]
search -- search for a keyword in charts
show -- show information of a chart
status -- displays the status of the named release
# Without descriptions
$ helm s[tab]
search show status
```
*Note*: Because of backwards-compatibility requirements, we were forced to have a different API to disable completion descriptions between `Zsh` and `Fish`.
### Limitations
* Custom completions implemented in Bash scripting (legacy) are not supported and will be ignored for `zsh` (including the use of the `BashCompCustom` flag annotation).
* You should instead use `ValidArgsFunction` and `RegisterFlagCompletionFunc()` which are portable to the different shells (`bash`, `zsh`, `fish`).
* The function `MarkFlagCustom()` is not supported and will be ignored for `zsh`.
* You should instead use `RegisterFlagCompletionFunc()`.
### Zsh completions standardization
Cobra 1.1 standardized its zsh completion support to align it with its other shell completions. Although the API was kept backwards-compatible, some small changes in behavior were introduced.
Please refer to [Zsh Completions](zsh_completions.md) for details.
## Fish completions
Cobra supports native Fish completions generated from the root `cobra.Command`. You can use the `command.GenFishCompletion()` or `command.GenFishCompletionFile()` functions. You must provide these functions with a parameter indicating if the completions should be annotated with a description; Cobra will provide the description automatically based on usage information. You can choose to make this option configurable by your users.
```
# With descriptions
$ helm s[tab]
search (search for a keyword in charts) show (show information of a chart) status (displays the status of the named release)
# Without descriptions
$ helm s[tab]
search show status
```
*Note*: Because of backwards-compatibility requirements, we were forced to have a different API to disable completion descriptions between `Zsh` and `Fish`.
### Limitations
* Custom completions implemented in Bash scripting (legacy) are not supported and will be ignored for `fish` (including the use of the `BashCompCustom` flag annotation).
* You should instead use `ValidArgsFunction` and `RegisterFlagCompletionFunc()` which are portable to the different shells (`bash`, `zsh`, `fish`).
* The function `MarkFlagCustom()` is not supported and will be ignored for `fish`.
* You should instead use `RegisterFlagCompletionFunc()`.
* The following flag completion annotations are not supported and willbe ignored for `fish`:
*`BashCompFilenameExt` (filtering by file extension)
*`BashCompSubdirsInDir` (filtering by directory)
* The functions corresponding to the above annotations are consequently not supported and will be ignored for `fish`:
*`MarkFlagFilename()` and `MarkPersistentFlagFilename()` (filtering by file extension)
*`MarkFlagDirname()` and `MarkPersistentFlagDirname()` (filtering by directory)
* Similarly, the following completion directives are not supported and will be ignored for `fish`:
*`ShellCompDirectiveFilterFileExt` (filtering by file extension)
*`ShellCompDirectiveFilterDirs` (filtering by directory)
## PowerShell completions
Please refer to [PowerShell Completions](powershell_completions.md) for details.
