Cannot instal gettext 1.2.0 gem


OS = CentOS4.2
Ruby = 1.8.4
Gem = 0.8.11

When attempting to install gettext I get the following error:

gem install gettext

Attempting local installation of ‘gettext’
Local gem file not found: gettext*.gem
Attempting remote installation of ‘gettext’
Select which gem to install for your platform (i386-linux)

  1. gettext 1.2.0 (ruby)
  2. gettext 1.2.0 (mswin32)
  3. gettext 1.1.1 (mswin32)
  4. gettext 1.1.1 (ruby)
  5. gettext 1.1.0 (mswin32)
  6. gettext 1.1.0 (ruby)
  7. gettext 1.0.0 (mswin32)
  8. gettext 1.0.0 (ruby)
  9. Cancel installation

Building native extensions. This could take a while…
can’t find header files for ruby.
ERROR: While executing gem … (RuntimeError)
ERROR: Failed to build gem native extension.
Gem files will remain installed in
/usr/lib/ruby/gems/1.8/gems/gettext-1.2.0 for inspection.
ruby extconf.rb install gettext\n

Results logged to

cat /usr/lib/ruby/gems/1.8/gems/gettext-1.2.0/ext/gettext/gem_make.out

ruby extconf.rb install gettext

What am I doing wrong?