copier/docs/generating.md
Tomasz Pluskiewicz 8b43355889 clarify the --vcs-ref HEAD usage
closes #787
2022-09-15 17:11:41 +01:00

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# Generating a project
!!! warning
Generate projects only from trusted templates as their tasks run with the
same level of access as your user.
As seen in the quick usage section, you can generate a project from a template using the
`copier` command-line tool:
```shell
copier path/to/project/template path/to/destination
```
Or within Python code:
```python
copier.run_auto("path/to/project/template", "path/to/destination")
```
The "template" parameter can be a local path, an URL, or a shortcut URL:
- GitHub: `gh:namespace/project`
- GitLab: `gl:namespace/project`
Use the `--data` command-line argument or the `data` parameter of the
`copier.run_auto()` function to pass whatever extra context you want to be available in
the templates. The arguments can be any valid Python value, even a function.
Use the `--vcs-ref` command-line argument to checkout a particular Git ref before
generating the project.
[All the available options][copier.cli] are described with the `--help-all` option.
## Templates versions
By default, Copier will copy from the last release found in template Git tags, sorted as
[PEP 440](https://peps.python.org/pep-0440/), regardless of whether the template is from
a URL or a local clone of a Git repository.
The exception to this is if you use a local clone of a template repository that has had
any modifications made, in this case Copier will use this modified working copy of the
template to aid development of new template features.
If you would like to override the version of template being installed, the
[`--vcs-ref`](../configuring/#vcs_ref) argument can be used to specify a branch, tag or
other reference to use.
For example to use the latest master branch from a public repository:
```shell
copier --vcs-ref master https://github.com/foo/copier-template.git ./path/to/destination
```
Or to work from the current checked out revision of a local template:
```shell
copier --vcs-ref HEAD path/to/project/template path/to/destination
```
!!! tip
If there are uncommited changes in the local template, they will be included in the `HEAD`
ref
## Regenerating a project
When you execute `copier copy $template $project` again over a preexisting `$project`,
Copier will just "recopy" it, ignoring previous history.
!!! warning
This is not [the recommended approach for updating a project][updating-a-project],
where you usually want Copier to respect the project evolution wherever it doesn't
conflict with the template evolution.