site/docs/windows.md

---
layout: documentation
title: Windows
---

# Using Bazel on Windows

Bazel runs on 64 bit Windows 7 or higher. Known issues are [marked with label
"Windows"](https://github.com/bazelbuild/bazel/issues?q=is%3Aissue+is%3Aopen+label%3A%22category%3A+multi-platform+%3E+windows%22)
on GitHub issues.

Bazel is a native Windows binary. Run it from the Windows Command Prompt
(`cmd.exe`) or from PowerShell.

## <a name="requirements"></a>Requirements

*   Python 2.7 or later.
*   [msys2 shell](https://msys2.github.io/).

    You also need to set the `BAZEL_SH` environment variable to point to
    `bash.exe`. For example in the Windows Command Prompt (`cmd.exe`):

    ```
    set BAZEL_SH=C:\msys64\usr\bin\bash.exe
    ```

*   Several msys2 packages.

    Run the following command in the msys2 shell to install them:

    ```bash
    pacman -Syuu git curl zip unzip
    ```

*   Java JDK 8.

    JDK 7 and 9 are not supported.

    If you downloaded a binary distribution of Bazel (see [installing Bazel on
    Windows](install-windows.html)), the binary has JDK 8 embedded by default.

*   If you built Bazel from source: set the `JAVA_HOME` environment variable to
    the JDK's directory.

    For example in the Windows Command Prompt (`cmd.exe`):

    ```
    set JAVA_HOME=C:\Program Files\Java\jdk1.8.0_112
    ```

    This step is not required if you downloaded a binary distribution of Bazel
    or installed Bazel using Chocolatey. See [installing Bazel on
    Windows](install-windows.html).

Environment variables you set in the Windows Command Prompt (`cmd.exe`) are only
set in that command prompt session. If you start a new `cmd.exe`, you need to
set the variables again. To always set the variables when `cmd.exe` starts, you
can add them to the User variables or System variables in the `Control Panel >
System Properties > Advanced > Environment Variables...` dialog box.

## <a name="install"></a>Installation

See [Install Bazel on Windows](install-windows.html) for installation
instructions.

## <a name="using"></a>Using Bazel on Windows

The first time you build any target, Bazel auto-configures the location of
Python and the Visual C++ compiler. If you need to auto-configure again, run
`bazel clean` then build a target.

### Build C++

To build C++ targets, you need:

*   The Visual C++ compiler.

    You can install it in one of the following ways:

    *   Install [Visual Studio 2015 or later](https://www.visualstudio.com/)
        (Community Edition is enough) with Visual C++.

        Make sure to also install the `Visual C++ > Common Tools for Visual C++`
        and `Visual C++ > Microsoft Foundation Classes for C++` features. These
        features are not installed by default.

    *   Install the [Visual C++ Build
        Tools 2015 or later](http://landinghub.visualstudio.com/visual-cpp-build-tools).

*   The `BAZEL_VS` or `BAZEL_VC` environment variable.

    Bazel tries to locate the C++ compiler the first time you build any
    target. To tell Bazel where the compiler is, you can set one of the
    following environment variables:

    *   `BAZEL_VS` storing the Visual Studio installation directory

    *   `BAZEL_VC` storing the Visual C++ Build Tools installation directory

    Setting one of these variables is enough. For example:

    ```
    set BAZEL_VS=C:\Program Files (x86)\Microsoft Visual Studio 14.0
    ```

    or

    ```
    set BAZEL_VC=C:\Program Files (x86)\Microsoft Visual Studio\2017\BuildTools\VC
    ```

*   The [Windows
    SDK](https://developer.microsoft.com/en-us/windows/downloads/windows-10-sdk).

    The Windows SDK contains header files and libraries you need when building
    Windows applications, including Bazel itself.

If everything is set up, you can build a C++ target now!

Try building a target from one of our [sample
projects](https://github.com/bazelbuild/bazel/tree/master/examples):

```
C:\projects\bazel> bazel build //examples/cpp:hello-world

C:\projects\bazel> bazel-bin\examples\cpp\hello-world.exe
```

### Build Java

There's no setup necessary.

On Windows, Bazel builds three output files for `java_binary` rules:

*   a `.jar` file
*   a shell script that can set up the environment for the JVM and run the
    binary
*   a `.cmd` file (a batch script) that can call Bash with the aforementioned
    shell script.

Try building a target from one of our [sample
projects](https://github.com/bazelbuild/bazel/tree/master/examples):

```
C:\projects\bazel> bazel build //examples/java-native/src/main/java/com/example/myproject:hello-world

C:\projects\bazel> bazel-bin\examples\java-native\src\main\java\com\example\myproject\hello-world.cmd
```

### Build Python

To build Python targets, you need:

*   The [Python interpreter](https://www.python.org/downloads/)

    Both Python 2 and Python 3 are supported.

    To tell Bazel where Python is, you can use `--python_path=<path/to/python>`.
    For example:

    ```
    bazel build --python_path=C:/Python27/python.exe ...
    ```

    If `--python_path` is not specified, Bazel uses `python.exe` as
    the interpreter and the binary looks for it in `$PATH` during runtime.
    If it is not in `$PATH`(for example, when you use `py_binary` as an action's
    executable, Bazel will sanitize `$PATH`), then the execution will fail.


On Windows, Bazel builds two output files for `py_binary` rules:

*   a self-extracting zip file
*   a batch script that can execute the Python interpreter with the
    self-extracting zip file as the argument

You can either run the batch script (it has a `.cmd` extension) or you can run
Python with the self-extracting zip file as the argument.

Try building a target from one of our [sample
projects](https://github.com/bazelbuild/bazel/tree/master/examples):

```
C:\projects\bazel> bazel build //examples/py_native:bin

C:\projects\bazel> bazel-bin\examples\py_native\bin.cmd

C:\projects\bazel> python bazel-bin\examples\py_native\bin
```

If you are interested in details about how Bazel builds Python targets on
Windows, check out this [design
doc](https://bazel.build/designs/2016/09/05/build-python-on-windows.html).