Docker: How to Use Bash with an Alpine Based Docker Image

TLDR

Alpine Linux images use sh (BusyBox shell) by default, not bash. To use bash, install it with apk add --no-cache bash in your Dockerfile or at runtime. Then you can run scripts or open an interactive bash shell as needed.

Why Alpine Uses sh Instead of bash

Alpine is designed to be lightweight and secure, so it ships with BusyBox's sh shell by default. This keeps images small, but means bash isn't available unless you add it yourself.

How to Install bash in an Alpine Container

Add this line to your Dockerfile:

RUN apk add --no-cache bash

Example Dockerfile:

FROM alpine:3.20
RUN apk add --no-cache bash
CMD ["bash"]

Or, for a one-off interactive session:

docker run -it alpine:3.20 sh
# Inside the container:
apk add --no-cache bash
bash

Running Scripts with bash

If your script uses bash features (like arrays or advanced syntax), make sure to:

• Install bash as above
• Use #!/bin/bash as the shebang in your script
• Run the script with bash script.sh or make it executable

Best Practices

• Only install bash if you need it—stick with sh for simple scripts to keep images small
• For multi-stage builds, install bash only in build stages if possible
• Document the shell requirements for your scripts

Troubleshooting

• If you see bash: not found, install it with apk add --no-cache bash
• If your script fails with syntax errors, check the shebang and shell compatibility

Conclusion

To use bash in Alpine-based Docker images, just install it with apk and use it as needed. This gives you access to familiar bash features while keeping your images lean and efficient.