Shell Completion¶
Click provides tab completion support for Bash (version 4.4 and up), Zsh, and Fish. It is possible to add support for other shells too, and suggestions can be customized at multiple levels.
Shell completion suggests command names, option names, and values for choice, file, and path parameter types. Options are only listed if at least a dash has been entered. Hidden commands and options are not shown.
$ repo <TAB><TAB>
clone commit copy delete setuser
$ repo clone -<TAB><TAB>
--deep --help --rev --shallow -r
Enabling Completion¶
Completion is only available if a script is installed and invoked
through an entry point, not through the python
command. See
Setuptools Integration. Once the executable is installed, calling it with
a special environment variable will put Click in completion mode.
To enable shell completion, the user needs to register a special
function with their shell. The exact script varies depending on the
shell you are using. Click will output it when called with
_{FOO_BAR}_COMPLETE
set to {shell}_source
. {FOO_BAR}
is
the executable name in uppercase with dashes replaced by underscores.
It is conventional but not strictly required for environment variable
names to be in upper case. This convention helps distinguish environment
variables from regular shell variables and commands, making scripts
and configuration files more readable and easier to maintain. The
built-in shells are bash
, zsh
, and fish
.
Provide your users with the following instructions customized to your
program name. This uses foo-bar
as an example.
Add this to ~/.bashrc
:
eval "$(_FOO_BAR_COMPLETE=bash_source foo-bar)"
Add this to ~/.zshrc
:
eval "$(_FOO_BAR_COMPLETE=zsh_source foo-bar)"
Add this to ~/.config/fish/completions/foo-bar.fish
:
_FOO_BAR_COMPLETE=fish_source foo-bar | source
This is the same file used for the activation script method below. For Fish it’s probably always easier to use that method.
Using eval
means that the command is invoked and evaluated every
time a shell is started, which can delay shell responsiveness. To speed
it up, write the generated script to a file, then source that. You can
generate the files ahead of time and distribute them with your program
to save your users a step.
Save the script somewhere.
_FOO_BAR_COMPLETE=bash_source foo-bar > ~/.foo-bar-complete.bash
Source the file in ~/.bashrc
.
. ~/.foo-bar-complete.bash
Save the script somewhere.
_FOO_BAR_COMPLETE=zsh_source foo-bar > ~/.foo-bar-complete.zsh
Source the file in ~/.zshrc
.
. ~/.foo-bar-complete.zsh
Save the script to ~/.config/fish/completions/foo-bar.fish
:
_FOO_BAR_COMPLETE=fish_source foo-bar > ~/.config/fish/completions/foo-bar.fish
After modifying the shell config, you need to start a new shell in order for the changes to be loaded.
Custom Type Completion¶
When creating a custom ParamType
, override its
shell_complete()
method to provide shell
completion for parameters with the type. The method must return a list
of CompletionItem
objects. Besides the value, these objects
hold metadata that shell support might use. The built-in implementations
use type
to indicate special handling for paths, and help
for
shells that support showing a help string next to a suggestion.
In this example, the type will suggest environment variables that start with the incomplete value.
class EnvVarType(ParamType):
name = "envvar"
def shell_complete(self, ctx, param, incomplete):
return [
CompletionItem(name)
for name in os.environ if name.startswith(incomplete)
]
@click.command()
@click.option("--ev", type=EnvVarType())
def cli(ev):
click.echo(os.environ[ev])
Overriding Value Completion¶
Value completions for a parameter can be customized without a custom
type by providing a shell_complete
function. The function is used
instead of any completion provided by the type. It is passed 3 keyword
arguments:
ctx
- The current command context.param
- The current parameter requesting completion.incomplete
- The partial word that is being completed. May be an empty string if no characters have been entered yet.
It must return a list of CompletionItem
objects, or as a
shortcut it can return a list of strings.
In this example, the command will suggest environment variables that start with the incomplete value.
def complete_env_vars(ctx, param, incomplete):
return [k for k in os.environ if k.startswith(incomplete)]
@click.command()
@click.argument("name", shell_complete=complete_env_vars)
def cli(name):
click.echo(f"Name: {name}")
click.echo(f"Value: {os.environ[name]}")
Adding Support for a Shell¶
Support can be added for shells that do not come built in. Be sure to check PyPI to see if there’s already a package that adds support for your shell. This topic is very technical, you’ll want to look at Click’s source to study the built-in implementations.
Shell support is provided by subclasses of ShellComplete
registered with add_completion_class()
. When Click is invoked in
completion mode, it calls source()
to output the
completion script, or complete()
to output
completions. The base class provides default implementations that
require implementing some smaller parts.
First, you’ll need to figure out how your shell’s completion system
works and write a script to integrate it with Click. It must invoke your
program with the environment variable _{FOO_BAR}_COMPLETE
set to
{shell}_complete
and pass the complete args and incomplete value.
How it passes those values, and the format of the completion response
from Click is up to you.
In your subclass, set source_template
to the
completion script. The default implementation will perform %
formatting with the following variables:
complete_func
- A safe name for the completion function defined in the script.complete_var
- The environment variable name for passing the{shell}_complete
instruction.foo_bar
- The name of the executable being completed.
The example code is for a made up shell “My Shell” or “mysh” for short.
from click.shell_completion import add_completion_class
from click.shell_completion import ShellComplete
_mysh_source = """\
%(complete_func)s {
response=$(%(complete_var)s=mysh_complete %(foo_bar)s)
# parse response and set completions somehow
}
call-on-complete %(foo_bar)s %(complete_func)s
"""
@add_completion_class
class MyshComplete(ShellComplete):
name = "mysh"
source_template = _mysh_source
Next, implement get_completion_args()
. This must
get, parse, and return the complete args and incomplete value from the
completion script. For example, for the Bash implementation the
COMP_WORDS
env var contains the command line args as a string, and
the COMP_CWORD
env var contains the index of the incomplete arg. The
method must return a (args, incomplete)
tuple.
import os
from click.parser import split_arg_string
class MyshComplete(ShellComplete):
...
def get_completion_args(self):
args = split_arg_string(os.environ["COMP_WORDS"])
if os.environ["COMP_PARTIAL"] == "1":
incomplete = args.pop()
return args, incomplete
return args, ""
Finally, implement format_completion()
. This is
called to format each CompletionItem
into a string. For
example, the Bash implementation returns f"{item.type},{item.value}
(it doesn’t support help strings), and the Zsh implementation returns
each part separated by a newline, replacing empty help with a _
placeholder. This format is entirely up to what you parse with your
completion script.
The type
value is usually plain
, but it can be another value
that the completion script can switch on. For example, file
or
dir
can tell the shell to handle path completion, since the shell is
better at that than Click.
class MyshComplete(ShellComplete):
...
def format_completion(self, item):
return f"{item.type}\t{item.value}"
With those three things implemented, the new shell support is ready. In case those weren’t sufficient, there are more parts that can be overridden, but that probably isn’t necessary.
The activation instructions will again depend on how your shell works. Use the following to generate the completion script, then load it into the shell somehow.
_FOO_BAR_COMPLETE=mysh_source foo-bar