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# Version CLI Option, `is_eager`
You could use a callback to implement a `--version` *CLI option*.
It would show the version of your CLI program and then it would terminate it. Even before any other *CLI parameter* is processed.
## First version of `--version`
Let's see a first version of how it could look like:
{* docs_src/options/version/tutorial001_an.py hl[9:12,17:19] *}
/// tip
Notice that we don't have to get the `typer.Context` and check for `ctx.resilient_parsing` for completion to work, because we only print and modify the program when `--version` is passed, otherwise, nothing is printed or changed from the callback.
///
If the `--version` *CLI option* is passed, we get a value `True` in the callback.
Then we can print the version and raise `typer.Exit()` to make sure the program is terminated before anything else is executed.
We also declare the explicit *CLI option* name `--version`, because we don't want an automatic `--no-version`, it would look awkward.
Check it:
<div class="termy">
```console
$ python main.py --help
// We get a --version, and don't get an awkward --no-version 🎉
Usage: main.py [OPTIONS]
Options:
--version
--name TEXT
--help Show this message and exit.
// We can call it normally
$ python main.py --name Camila
Hello Camila
// And we can get the version
$ python main.py --version
Awesome CLI Version: 0.1.0
// Because we exit in the callback, we don't get a "Hello World" message after the version 🚀
```
</div>
## Previous parameters and `is_eager`
But now let's say that the `--name` *CLI option* that we declared before `--version` is required, and it has a callback that could exit the program:
{* docs_src/options/version/tutorial002_an.py hl[15:17,22:24] *}
Then our CLI program could not work as expected in some cases as it is *right now*, because if we use `--version` after `--name` then the callback for `--name` will be processed before and we can get its error:
<div class="termy">
```console
$ python main.py --name Rick --version
Only Camila is allowed
Aborted!
```
</div>
/// tip
We don't have to check for `ctx.resilient_parsing` in the `name_callback()` for completion to work, because we are not using `typer.echo()`, instead we are raising a `typer.BadParameter`.
///
/// note | Technical Details
`typer.BadParameter` prints the error to "standard error", not to "standard output", and because the completion system only reads from "standard output", it won't break completion.
///
/// info
If you need a refresher about what is "standard output" and "standard error" check the section in [Printing and Colors: "Standard Output" and "Standard Error"](../printing.md#standard-output-and-standard-error){.internal-link target=_blank}.
///
### Fix with `is_eager`
For those cases, we can mark a *CLI parameter* (a *CLI option* or *CLI argument*) with `is_eager=True`.
That will tell **Typer** (actually Click) that it should process this *CLI parameter* before the others:
{* docs_src/options/version/tutorial003_an.py hl[23:26] *}
Check it:
<div class="termy">
```console
$ python main.py --name Rick --version
// Now we only get the version, and the name is not used
Awesome CLI Version: 0.1.0
```
</div>
|
