RbConfigというのがあってビルド時の情報とかが取れる
Rubyのインストール時の情報を保持しているみたい
RbConfig::CONFIGという定数のHashに様々な情報が入っている。
sugamasao@GRAM% ruby -v ruby 1.9.3p5 (2011-11-30 revision 33907) [x86_64-darwin10.8.0] sugamasao@GRAM% ruby -rpp -e"pp RbConfig::CONFIG" {"DESTDIR"=>"", "MAJOR"=>"1", "MINOR"=>"9", "TEENY"=>"1", "PATCHLEVEL"=>"5", "INSTALL"=>"/usr/bin/install -c", "EXEEXT"=>"", "prefix"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head", "ruby_install_name"=>"ruby", "RUBY_INSTALL_NAME"=>"ruby", "RUBY_SO_NAME"=>"ruby.1.9.1", "exec"=>"exec", "ruby_pc"=>"ruby-1.9.pc", "PACKAGE"=>"ruby", "BUILTIN_TRANSSRCS"=>" newline.c", "USE_RUBYGEMS"=>"YES", "MANTYPE"=>"doc", "NROFF"=>"/usr/bin/nroff", "vendorhdrdir"=> "/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/include/ruby-1.9.1/vendor_ruby", "sitehdrdir"=> "/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/include/ruby-1.9.1/site_ruby", "rubyhdrdir"=> "/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/include/ruby-1.9.1", "UNIVERSAL_INTS"=>"", "UNIVERSAL_ARCHNAMES"=>"", "configure_args"=> " '--prefix=/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head' '--enable-shared' '--disable-install-doc' '--with-libyaml-dir=/Users/sugamasao/.rvm/usr' '--with-baseruby=/Users/sugamasao/.rvm/wrappers/ruby-1.8.7-head/ruby' 'CC=clang'", "vendordir"=> "/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/lib/ruby/vendor_ruby", "sitedir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/lib/ruby/site_ruby", "ruby_version"=>"1.9.1", "sitearch"=>"x86_64-darwin10.8.0", "arch"=>"x86_64-darwin10.8.0", "RI_BASE_NAME"=>"ri", "ridir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/share/ri", "rubylibprefix"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/lib/ruby", "MAKEFILES"=>"Makefile", "THREAD_MODEL"=>"pthread", "SYMBOL_PREFIX"=>"_", "EXPORT_PREFIX"=>"", "COMMON_HEADERS"=>"", "COMMON_MACROS"=>"", "COMMON_LIBS"=>"", "MAINLIBS"=>"", "ENABLE_SHARED"=>"yes", "DLDLIBS"=>"", "SOLIBS"=>"", "LIBRUBYARG_SHARED"=>"-lruby.1.9.1", "LIBRUBYARG_STATIC"=>"-lruby.1.9.1-static", "LIBRUBYARG"=>"-lruby.1.9.1", "LIBRUBY"=>"libruby.1.9.1.dylib", "LIBRUBY_ALIASES"=>"libruby.1.9.dylib libruby.dylib", "LIBRUBY_SO"=>"libruby.1.9.1.dylib", "LIBRUBY_A"=>"libruby.1.9.1-static.a", "RUBYW_INSTALL_NAME"=>"", "rubyw_install_name"=>"", "LIBRUBY_DLDFLAGS"=> "-Wl,-undefined,dynamic_lookup -Wl,-multiply_defined,suppress -Wl,-flat_namespace -install_name /Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/lib/libruby.1.9.1.dylib -current_version 1.9.1 -compatibility_version 1.9.1 -Wl,-unexported_symbol,_Init_* -Wl,-unexported_symbol,*_threadptr_* $(XLDFLAGS)", "LIBRUBY_LDSHARED"=>"clang -dynamiclib", "warnflags"=> "-Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Werror=pointer-arith -Werror=write-strings -Werror=declaration-after-statement -Werror=shorten-64-to-32 -Werror=implicit-function-declaration", "debugflags"=>"-ggdb", "optflags"=>"-O3", "cxxflags"=> " -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Werror=pointer-arith -Werror=write-strings -Werror=declaration-after-statement -Werror=shorten-64-to-32 -Werror=implicit-function-declaration", "cflags"=> " -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Werror=pointer-arith -Werror=write-strings -Werror=declaration-after-statement -Werror=shorten-64-to-32 -Werror=implicit-function-declaration", "cppflags"=>"", "NULLCMD"=>":", "INSTALLDOC"=>"nodoc", "CAPITARGET"=>"nodoc", "RDOCTARGET"=>"nodoc", "EXECUTABLE_EXTS"=>"", "ARCHFILE"=>"", "LIBRUBY_RELATIVE"=>"no", "EXTOUT"=>".ext", "PREP"=>"miniruby", "TEST_RUNNABLE"=>"yes", "setup"=>"Setup", "EXTSTATIC"=>"", "STRIP"=>"strip -A -n", "TRY_LINK"=>"", "LIBPATHENV"=>"DYLD_LIBRARY_PATH", "RPATHFLAG"=>"", "LIBPATHFLAG"=>" -L%s", "LINK_SO"=>"", "LIBEXT"=>"a", "DLEXT2"=>"", "DLEXT"=>"bundle", "LDSHAREDXX"=>"g++ -dynamic -bundle", "LDSHARED"=>"clang -dynamic -bundle", "CCDLFLAGS"=>"-fno-common", "STATIC"=>"", "ARCH_FLAG"=>"", "DLDFLAGS"=> "-Wl,-undefined,dynamic_lookup -Wl,-multiply_defined,suppress -Wl,-flat_namespace", "ALLOCA"=>"", "WERRORFLAG"=>"-Werror", "CHDIR"=>"cd -P", "RMALL"=>"rm -fr", "RMDIRS"=>"rmdir -p", "RMDIR"=>"rmdir", "CP"=>"cp", "RM"=>"rm -f", "PKG_CONFIG"=>"", "DOXYGEN"=>"", "DOT"=>"", "MAKEDIRS"=>"mkdir -p", "MKDIR_P"=>"mkdir -p", "INSTALL_DATA"=>"/usr/bin/install -c -m 644", "INSTALL_SCRIPT"=>"/usr/bin/install -c", "INSTALL_PROGRAM"=>"/usr/bin/install -c", "SET_MAKE"=>"", "LN_S"=>"ln -s", "NM"=>"nm", "DLLWRAP"=>"", "WINDRES"=>"", "OBJCOPY"=>":", "OBJDUMP"=>"", "ASFLAGS"=>"", "AS"=>"as", "AR"=>"ar", "RANLIB"=>"ranlib", "try_header"=>"", "COUTFLAG"=>"-o ", "OUTFLAG"=>"-o ", "CPPOUTFILE"=>"-o conftest.i", "GNU_LD"=>"no", "GCC"=>"yes", "EGREP"=>"/usr/bin/grep -E", "GREP"=>"/usr/bin/grep", "CPP"=>"clang -E", "CXXFLAGS"=> " -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Werror=pointer-arith -Werror=write-strings -Werror=declaration-after-statement -Werror=shorten-64-to-32 -Werror=implicit-function-declaration", "CXX"=>"g++", "OBJEXT"=>"o", "CPPFLAGS"=>"-D_XOPEN_SOURCE -D_DARWIN_C_SOURCE ", "LDFLAGS"=>"-L. ", "CFLAGS"=> " -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Werror=pointer-arith -Werror=write-strings -Werror=declaration-after-statement -Werror=shorten-64-to-32 -Werror=implicit-function-declaration -fno-common -pipe", "CC"=>"clang", "target_os"=>"darwin10.8.0", "target_vendor"=>"apple", "target_cpu"=>"x86_64", "target"=>"x86_64-apple-darwin10.8.0", "host_os"=>"darwin10.8.0", "host_vendor"=>"apple", "host_cpu"=>"x86_64", "host"=>"x86_64-apple-darwin10.8.0", "RUBYW_BASE_NAME"=>"rubyw", "RUBY_BASE_NAME"=>"ruby", "build_os"=>"darwin10.8.0", "build_vendor"=>"apple", "build_cpu"=>"x86_64", "build"=>"x86_64-apple-darwin10.8.0", "RUBY_RELEASE_DATE"=>"2011-11-30", "RUBY_PROGRAM_VERSION"=>"1.9.3", "BASERUBY"=>"/Users/sugamasao/.rvm/wrappers/ruby-1.8.7-head/ruby", "target_alias"=>"", "host_alias"=>"", "build_alias"=>"", "LIBS"=>"-lpthread -ldl -lobjc", "ECHO_T"=>"", "ECHO_N"=>"", "ECHO_C"=>"\\\\c", "DEFS"=>"", "mandir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/share/man", "localedir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/share/locale", "libdir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/lib", "psdir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/share/doc/ruby", "pdfdir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/share/doc/ruby", "dvidir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/share/doc/ruby", "htmldir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/share/doc/ruby", "infodir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/share/info", "docdir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/share/doc/ruby", "oldincludedir"=>"/usr/include", "includedir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/include", "localstatedir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/var", "sharedstatedir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/com", "sysconfdir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/etc", "datadir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/share", "datarootdir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/share", "libexecdir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/libexec", "sbindir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/sbin", "bindir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/bin", "exec_prefix"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head", "PACKAGE_URL"=>"", "PACKAGE_BUGREPORT"=>"", "PACKAGE_STRING"=>"", "PACKAGE_VERSION"=>"", "PACKAGE_TARNAME"=>"", "PACKAGE_NAME"=>"", "PATH_SEPARATOR"=>":", "SHELL"=>"/bin/sh", "rubylibdir"=>"/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/lib/ruby/1.9.1", "archdir"=> "/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/lib/ruby/1.9.1/x86_64-darwin10.8.0", "sitelibdir"=> "/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/lib/ruby/site_ruby/1.9.1", "sitearchdir"=> "/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/lib/ruby/site_ruby/1.9.1/x86_64-darwin10.8.0", "vendorlibdir"=> "/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/lib/ruby/vendor_ruby/1.9.1", "vendorarchdir"=> "/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/lib/ruby/vendor_ruby/1.9.1/x86_64-darwin10.8.0", "topdir"=> "/Users/sugamasao/.rvm/rubies/ruby-1.9.3-head/lib/ruby/1.9.1/x86_64-darwin10.8.0"}
ちなみに、元々はConfigのエイリアスとしてRbConfigっていうのがあったっぽいけど*1、Ruby1.9.3（から？）だと、逆にConfigの方がエイリアスになっているらしく、RbConfigを使うことが推奨されている。
Configを使うと、プギャー！ってされるのだった。
ruby-1.9.3-head :001 > Config (irb):1: Use RbConfig instead of obsolete and deprecated Config.
みんな大好きwatchrもConfig(RbConfigじゃないので使うと警告がでるのであった)を使っていて、OS毎のファイルイベントを扱うライブラリの選択とかの参考にしてる感じ。
*1:ruby1.8時代のマニュアルのニュアンスだと
