rash

Rash is a lightweight, container-friendly shell scripting language that uses a declarative YAML syntax inspired by Ansible. It brings the simplicity and readability of Ansible playbooks to local scripting and container entrypoints, all in a single Rust binary with no dependencies.

Why Rash?

• Declarative vs Imperative: Define what your script should accomplish, not how
• Container-Optimized: Single binary with no dependencies, perfect for minimal containers
• Lightweight: Runs on any Linux system, even resource-constrained IoT devices
• Template-Powered: Uses MiniJinja for powerful templating capabilities
• Intuitive Syntax: Familiar YAML structure for those who know Ansible
• Built-in Command-Line Parsing: Elegant docopt implementation for clean script interfaces
• Modular Design: Focused modules for different tasks

Example: Imperative vs Declarative

Bash (Imperative)

#!/bin/bash
set -e

# Validate required environment variables
REQUIRED_PARAMS="
DATABASE_URL
DATABASE_USER
DATABASE_PASSWORD
LOG_LEVEL
"

for required in $REQUIRED_PARAMS ; do
  [[ -z "${!required}" ]] && echo "$required IS NOT DEFINED" && exit 1
done

# Configure the application
echo "[$0] Configuring application..."
CONFIG_FILE="/app/config.json"
cat > $CONFIG_FILE << EOF
{
  "database": {
    "url": "$DATABASE_URL",
    "user": "$DATABASE_USER",
    "password": "$DATABASE_PASSWORD"
  },
  "server": {
    "port": "${SERVER_PORT:-8080}",
    "log_level": "$LOG_LEVEL"
  }
}
EOF

# Set correct permissions
chmod 0600 $CONFIG_FILE

echo "[$0] Starting application..."
exec "$@"

Rash (Declarative)

#!/usr/bin/env rash

- name: Verify input parameters
  assert:
    that:
      - env.DATABASE_URL is defined
      - env.DATABASE_USER is defined
      - env.DATABASE_PASSWORD is defined
      - env.LOG_LEVEL is defined

- name: Configure application
  template:
    src: config.j2
    dest: /app/config.json
    mode: "0600"
  vars:
    server_port: "{{ env.SERVER_PORT | default('8080') }}"

- name: Launch command
  command:
    cmd: "{{ rash.argv }}"
    transfer_pid: yes

Installation

Binary (Linux/macOS)

curl -s https://api.github.com/repos/rash-sh/rash/releases/latest \
    | grep browser_download_url \
    | grep $(uname -m) \
    | grep $(uname | tr '[:upper:]' '[:lower:]') \
    | grep -v musl \
    | cut -d '"' -f 4 \
    | xargs curl -s -L \
    | sudo tar xvz -C /usr/local/bin

Arch Linux (AUR)

yay -S rash

Cargo

cargo install rash_core

Docker

docker run --rm -v /usr/local/bin/:/output --entrypoint /bin/cp ghcr.io/rash-sh/rash:latest /bin/rash /output/

Key Features

Built-in Command-Line Interface Parser

#!/usr/bin/env -S rash --
#
# Copy files from source to dest dir
#
# Usage:
#   copy.rh [options] <source>... <dest>
#   copy.rh
#
# Options:
#   -h --help    show this help message and exit
#   --mode MODE  dest file permissions [default: 0644]

- copy:
    src: "{{ item }}"
    dest: "{{ dest }}/{{ item | split('/') | last }}"
    mode: "{{ options.mode }}"
  loop: "{{ source | default([]) }}"

Container Entrypoints

Perfect for creating maintainable container entrypoints that handle environment validation, configuration management, and service initialization:

FROM alpine:3.16

# Install rash binary
ADD https://github.com/rash-sh/rash/releases/download/v0.6.0/rash-x86_64-unknown-linux-musl.tar.gz /tmp/
RUN tar xvzf /tmp/rash-x86_64-unknown-linux-musl.tar.gz -C /usr/local/bin && \
    rm /tmp/rash-x86_64-unknown-linux-musl.tar.gz

# Add entrypoint script
COPY entrypoint.rh /entrypoint.rh
RUN chmod +x /entrypoint.rh

ENTRYPOINT ["/entrypoint.rh"]

Templating System

Access environment variables and use powerful filters:

- name: Configure application
  template:
    src: config.j2
    dest: /etc/app/config.json
  vars:
    app_port: "{{ env.PORT | default('8080') }}"
    app_log_level: "{{ env.LOG_LEVEL | default('info') }}"
    database_url: "{{ env.DATABASE_URL }}"

Privilege Escalation

Run commands as different users with the built-in become functionality:

- name: Configure system DNS
  become: true
  copy:
    dest: /etc/resolv.conf
    content: |
      nameserver 208.67.222.222
      nameserver 208.67.220.220

Documentation

For comprehensive documentation, visit: https://rash-sh.github.io/docs/rash/master/

Community

• GitHub: https://github.com/rash-sh/rash
• Report Issues: https://github.com/rash-sh/rash/issues

License

Rash is distributed under the GPL-3.0 License.