Shell Scripts

Railpack can deploy applications that use shell scripts as their entry point.

Detection

Your project will be automatically detected as a shell script application if any of these conditions are met:

• A start.sh script exists in the root directory
• The RAILPACK_SHELL_SCRIPT environment variable is set to a valid script file

Script File

Create a shell script in your project root (e.g., start.sh):

#!/bin/bash

echo "Hello world..."

Shell Interpreter Detection

Railpack automatically detects which shell interpreter to use by reading the shebang line in your script. The following shells are supported:

Shell	Shebang Example	Notes
bash	#!/bin/bash	Available in base image
sh	#!/bin/sh	Available in base image
dash	#!/bin/dash	Available in base image (uses sh)
zsh	#!/bin/zsh	Automatically installed

If no shebang is present, sh is used as the default.

Unsupported Shells

Non-POSIX shells like fish, mksh, and ksh cannot be automatically detected and will fall back to bash. If you need to use these shells, you may need to install them manually in your script or use a supported shell.

Custom Installation

You can use the RAILPACK_INSTALL_CMD environment variable to run a custom installation command before the build step. This is useful for creating configuration files, downloading artifacts, or setting up the environment.

RAILPACK_INSTALL_CMD="mkdir -p config && echo 'production=true' > config/settings.conf"

You can also execute a custom script from your repository:

RAILPACK_INSTALL_CMD="bash setup.sh"

Files created during this step are available in the build step and the final image.

Additional Packages

You can install additional packages using the RAILPACK_PACKAGES environment variable for Mise-supported tools, and RAILPACK_BUILD_APT_PACKAGES or RAILPACK_DEPLOY_APT_PACKAGES for system packages.

RAILPACK_PACKAGES="jq@latest [email protected]"
RAILPACK_DEPLOY_APT_PACKAGES="ffmpeg"

For more details, see the environment variables documentation.

Config Variables

Variable	Description	Example
RAILPACK_SHELL_SCRIPT	Specify a custom shell script to execute	deploy.sh