Ruby Gem Docker Builder

A cross-platform script that builds Ruby gems with C extensions using Docker, creating precompiled versions compatible with modern systems.

Problem

Many legacy Ruby gems with C extensions fail to compile on modern macOS due to:

• Compiler compatibility issues
• Missing dependencies
• Architecture mismatches (ARM64 vs x86_64)
• Outdated build tools

Solution

This script uses Docker with Ruby 2.5 to:

1. Compile gems in a controlled Linux environment
2. Create precompiled versions that bypass compilation
3. Make gems work with both gem install and bundle install
4. Support any Ruby gem with C extensions

Requirements

• Docker (with ARM64 support on Apple Silicon)
• Ruby installed locally
• Bash shell

Usage

# Make executable
chmod +x build_ruby_gem.sh

# Build any gem with C extensions
./build_ruby_gem.sh <gem_name> <gem_version>

Examples

# Legacy gems that often fail on modern macOS
./build_ruby_gem.sh semacode-ruby19 0.7.4
./build_ruby_gem.sh nokogiri 1.13.10
./build_ruby_gem.sh nio4r 2.3.1
./build_ruby_gem.sh mysql2 0.5.4
./build_ruby_gem.sh pg 1.4.5
./build_ruby_gem.sh sqlite3 1.6.0

What It Does

1. Downloads the gem source in Docker
2. Compiles C extensions with compatible toolchain
3. Removes extension source files (prevents recompilation)
4. Packages precompiled gem with .so files
5. Installs locally for immediate use

Output

• Gem installed and ready to require
• Works with Bundler (no compilation attempts)
• Precompiled gem saved in ./precompiled/

Common Use Cases

• Legacy Rails applications with old gem dependencies
• macOS development with problematic C extensions
• CI/CD pipelines needing reliable gem builds
• Apple Silicon compatibility for x86_64 gems

---

Note: This creates architecture-specific builds. Run on the target platform or use multi-arch Docker builds for cross-platform compatibility.