26 May 2011

Add true Readline to Ruby on OS X

I normally use OS X system Ruby. As of OS X 10.6.4, that is Ruby 1.8.7-p174. Sadly, system Ruby links against libedit instead of libreadline, which means I can't use any of my nice readline setup.

To fix that, you can install readline with MacPorts or by hand and then compile a new readline.bundle for Ruby to use. But I use Homebrew to manage my unix packages, so those instructions weren't quite enough for me.

Here's how to add true Readline compatibility to Ruby 1.8.7-p174 on OS X 10.6 using Homebrew.

# Install readline
brew install readline

# Download the readline extension
cd /tmp
svn co http://svn.ruby-lang.org/repos/ruby/tags/v1_8_7_174/ext/readline/

# Compile the bundle against homebrewed readline
make readline.o CFLAGS='-I/usr/local/Cellar/readline/6.1/include -DHAVE_RL_USERNAME_COMPLETION_FUNCTION'
cc -arch i386 -arch x86_64 -pipe -bundle -undefined dynamic_lookup -o readline.bundle readline.o -L/usr/local/Cellar/readline/6.1/lib -L/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib -L. -arch i386 -arch x86_64 -lruby -lreadline -lncurses -lpthread -ldl

# Move the bundle into the right place
cd /Library/Ruby/Site/1.8/universal-darwin10.0/
sudo mv readline.bundle readline.bundle.libedit
sudo mv /tmp/readline/readline.bundle ./readline.bundle

Tada! Working Readline support in Ruby, including IRB.