Can't install on OS X

[ghost]

$ sudo gem install camper_van
Password:
Building native extensions.  This could take a while...
ERROR:  Error installing camper_van:
    ERROR: Failed to build gem native extension.

/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby extconf.rb
mkmf.rb can't find header files for ruby at /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/ruby.h

Gem files will remain installed in /Library/Ruby/Gems/1.8/gems/eventmachine-0.12.10 for inspection.
Results logged to /Library/Ruby/Gems/1.8/gems/eventmachine-0.12.10/ext/gem_make.out

[ghost]

Installed XCode CLI tools and get this error now:

$ sudo gem install camper_van
Password:
Building native extensions.  This could take a while...
ERROR:  Error installing camper_van:
    ERROR: Failed to build gem native extension.

/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby extconf.rb
checking for rb_trap_immediate in ruby.h,rubysig.h... yes
checking for rb_thread_blocking_region()... yes
checking for inotify_init() in sys/inotify.h... yes
checking for writev() in sys/uio.h... yes
checking for rb_thread_check_ints()... yes
checking for rb_time_new()... yes
checking for sys/event.h... yes
checking for sys/queue.h... yes
checking for main() in -lssl... yes
checking for main() in -lcrypto... yes
checking for main() in -lC... yes
checking for openssl/ssl.h... yes
checking for openssl/err.h... yes
creating Makefile

make
c++ -I. -I. -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I. -DBUILD_FOR_RUBY -DHAVE_RB_TRAP_IMMEDIATE -DHAVE_RBTRAP -DHAVE_RB_THREAD_BLOCKING_REGION -DHAVE_TBR -DHAVE_INOTIFY_INIT -DHAVE_INOTIFY -DHAVE_WRITEV -DHAVE_WRITEV -DHAVE_RB_THREAD_CHECK_INTS -DHAVE_RB_TIME_NEW -DOS_UNIX -DHAVE_SYS_EVENT_H -DHAVE_SYS_QUEUE_H -DHAVE_KQUEUE -DHAVE_OPENSSL_SSL_H -DHAVE_OPENSSL_ERR_H -DWITH_SSL  -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -fno-common -arch i386 -arch x86_64 -g -Os -pipe -fno-common -DENABLE_DTRACE  -fno-common  -pipe -fno-common    -c binder.cpp
In file included from binder.cpp:20:
./project.h:117:10: fatal error: 'sys/inotify.h' file not found
#include <sys/inotify.h>
         ^
1 error generated.
make: *** [binder.o] Error 1

Gem files will remain installed in /Library/Ruby/Gems/1.8/gems/eventmachine-0.12.10 for inspection.
Results logged to /Library/Ruby/Gems/1.8/gems/eventmachine-0.12.10/ext/gem_make.out

[ghost]

I installed full XCode and get this error:

$ sudo gem install camper_van
Password:
Building native extensions.  This could take a while...
Building native extensions.  This could take a while...
Building native extensions.  This could take a while...
ERROR:  Error installing camper_van:
    camper_van requires Ruby version ~> 1.9.2.

[zerowidth]

Just as the error says... camper_van is only set up to run under ruby 1.9.2 or greater. Since you're using sudo, I assume you're trying to use OS X's system ruby. I'd suggest trying either rvm or rbenv to install different versions of ruby.