Executing Bash Commands in Bazel

Oct 13, 2025 by wbrum.org 1 views

Introduction

Bazel is a popular build tool used for building and testing software projects. It provides a flexible and scalable way to manage dependencies and build rules. However, sometimes you may need to execute a bash command as part of your build process. In this article, we will explore how to ask Bazel BUILD to execute a bash command.

Use Case

As a Bazel beginner, I was trying to achieve a specific use case in my project. I had a dependency on third-party libraries from artifacts, and I wanted to include some custom scripts as part of my build process. I needed to execute a bash command to download and install these libraries.

Why Bazel?

Bazel is a great choice for managing complex build processes, especially when dealing with multiple dependencies and custom scripts. Its rule-based architecture makes it easy to define and execute build steps. However, executing bash commands can be a bit tricky in Bazel.

Executing Bash Commands in Bazel

To execute a bash command in Bazel, you can use the sh rule provided by the rules_sh package. This package is a part of the Bazel ecosystem and provides a set of rules for executing shell commands.

Step 1: Add the `rules_sh` Package

First, you need to add the rules_sh package to your WORKSPACE file. You can do this by running the following command:

bazel config set //path/to/your/project:rules_sh //external/rules_sh

Step 2: Create a `BUILD` File

Next, create a BUILD file in the directory where you want to execute the bash command. In this file, you can define a sh rule that executes the bash command.

Example `BUILD` File

Here's an example BUILD file that executes a bash command:

load("@rules_sh//sh:sh.bzl", "sh")

sh(
    name = "download_libraries",
    args = ["bash", "download_libraries.sh"],
    tools = ["bash"],
)

In this example, we're defining a sh rule named download_libraries that executes the download_libraries.sh script using the bash tool.

Step 3: Create a `download_libraries.sh` Script

Next, create a download_libraries.sh script in the same directory as the BUILD file. This script will contain the bash command that you want to execute.

Example `download_libraries.sh` Script

Here's an example download_libraries.sh script:

#!/bin/bash

# Download and install third-party libraries
wget https://example.com/library.tar.gz
tar -xvf library.tar.gz
cd library
./install.sh

Step 4: Run the Bazel Build

Finally, run the Bazel build using the following command:

bazel build //path/to/your/project:download_libraries

This will execute the bash command defined in the download_libraries.sh script.

Conclusion

In this article, we explored how to ask Bazel BUILD to execute a bash command. We used the rules_sh package to define a sh rule that executes the bash command. We also created a BUILD file and a download_libraries.sh script to demonstrate the process. With these steps, you can easily execute bash commands as part of your Bazel build process.

Best Practices

Here are some best practices to keep in mind when executing bash commands in Bazel:

Use the rules_sh package to define sh rules.
Keep your bash scripts simple and focused on a single task.
Use the tools attribute to specify the tools required by your bash script.
Use the args attribute to specify the arguments passed to your bash script.
Use the name attribute to specify the name of your sh rule.

Common Issues

Here are some common issues you may encounter when executing bash commands in Bazel:

Error: sh rule not found: Make sure you've added the rules_sh package to your WORKSPACE file.
Error: bash tool not found: Make sure you've specified the bash tool in your sh rule.
Error: download_libraries.sh script not found: Make sure you've created the download_libraries.sh script in the same directory as the BUILD file.

Conclusion

Q: What is the `rules_sh` package and why do I need it to execute bash commands in Bazel?

A: The rules_sh package is a part of the Bazel ecosystem that provides a set of rules for executing shell commands. You need it to execute bash commands in Bazel because it provides the necessary infrastructure to define and execute shell rules.

Q: How do I add the `rules_sh` package to my `WORKSPACE` file?

A: To add the rules_sh package to your WORKSPACE file, run the following command:

bazel config set //path/to/your/project:rules_sh //external/rules_sh

Q: What is the difference between a `sh` rule and a `bash` rule in Bazel?

A: In Bazel, a sh rule is a generic rule for executing shell commands, while a bash rule is a specific rule for executing bash commands. You can use the sh rule to execute any shell command, while the bash rule is specifically designed for executing bash commands.

Q: How do I specify the tools required by my bash script in a `sh` rule?

A: To specify the tools required by your bash script in a sh rule, use the tools attribute. For example:

sh(
    name = "download_libraries",
    args = ["bash", "download_libraries.sh"],
    tools = ["bash"],
)

Q: How do I specify the arguments passed to my bash script in a `sh` rule?

A: To specify the arguments passed to your bash script in a sh rule, use the args attribute. For example:

sh(
    name = "download_libraries",
    args = ["bash", "download_libraries.sh", "--verbose"],
    tools = ["bash"],
)

Q: What is the `name` attribute in a `sh` rule and why do I need it?

A: The name attribute in a sh rule specifies the name of the rule. You need it to identify the rule and to use it in your build process.

Q: How do I create a `download_libraries.sh` script and where should I put it?

A: To create a download_libraries.sh script, simply create a new file with a .sh extension and add your bash commands to it. You should put the script in the same directory as your BUILD file.

Q: How do I run the Bazel build and execute the bash command?

A: To run the Bazel build and execute the bash command, use the following command:

bazel build //path/to/your/project:download_libraries

Q: What are some common issues I might encounter when executing bash commands in Bazel?

A: Some common issues you might encounter when executing bash commands in Bazel include:

Error: sh rule not found
Error: bash tool not found
Error: download_libraries.sh script not found

Q: How do I troubleshoot issues with executing bash commands in Bazel?

A: To troubleshoot issues with executing bash commands in Bazel, follow these steps:

Check the WORKSPACE file to ensure that the rules_sh package is added.
Check the BUILD file to ensure that the sh rule is defined correctly.
Check the download_libraries.sh script to ensure that it is in the correct location and has the correct permissions.
Check the Bazel build output for any error messages.

Conclusion

In this article, we've answered some frequently asked questions about executing bash commands in Bazel. We've covered topics such as adding the rules_sh package, specifying tools and arguments, creating a download_libraries.sh script, and troubleshooting common issues. By following these guidelines, you should be able to successfully execute bash commands in Bazel.