I got my shiny new MBP on Friday and spent a good part of the weekend installing software. I ran into a installation issue with RVM and Ruby and just want to post a fix in case anyone runs across it. Just to be clear, the issue seems to be with Lion and not Ruby in general.

I successfully installed RVM (Ruby Version Manager) but received a nasty error when installing Ruby 1.9.2. My error log looked like:

[2011-07-30 16:52:07] ./configure --prefix="/Users/Jeff/.rvm/usr" checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... config/install-sh -c -d
checking for gawk... no
checking for mawk... no
checking for nawk... no
checking for awk... awk
checking whether make sets $(MAKE)... no
checking for gcc... /usr/bin/gcc-4.2
checking whether the C compiler works... no
configure: error: in /Users/Jeff/.rvm/src/yaml-0.1.4':
configure: error: C compiler cannot create executables
See
config.log' for more details

Essentially it means that "no acceptable compiler could be found." There are a couple of problems with OS X Lion and Ruby. First, if you read the installation notes for RVM you'll see the following:

For Lion, Rubies should be built using gcc rather than llvm-gcc. Since /usr/bin/gcc is now linked to /usr/bin/llvm-gcc-4.2, add the following to your shell's start-up file: export CC=gcc-4.2

Lion sets the default compiler to LLVM so you'll need to change it to gcc for Ruby to compile sucessfully. Open .bash_profile and add:

export CC=/usr/bin/gcc-4.2

The second problem seems to be with Xcode. Just becuase I "installed" Xcode 4.1 from the App Store doesn't mean that it actually installed. To get Ruby to compile I had to launch Xcode and actually install Xcode. After that it compiled with no problem.