10.10 Yosemite Update:
Just enter in gcc or make on the command line! OSX will know that you do not have the command line tools and prompt you to install them!
To check if they exist, xcode-select -p the return value will be 2 if they do NOT exist, and 0 if they do (as well as the directory).
10.9 Mavericks Update:
Use pkgutil --pkg-info=com.apple.pkg.CLTools_Executables
10.8 Update:
Option 1: Rob Napier suggested to use pkgutil --pkg-info=com.apple.pkg.DeveloperToolsCLI, which is probably cleaner.
Option 2: Check inside /var/db/receipts/com.apple.pkg.DeveloperToolsCLI.plist for a reference to com.apple.pkg.DeveloperToolsCLI and it will list the version 4.5.0.
$ defaults read /var/db/receipts/com.apple.pkg.DeveloperToolsCLI.plist
{
InstallDate = "2012-12-26 22:45:54 +0000";
InstallPrefixPath = "/";
InstallProcessName = Xcode;
PackageFileName = "DeveloperToolsCLI.pkg";
PackageGroups = (
"com.apple.FindSystemFiles.pkg-group",
"com.apple.DevToolsBoth.pkg-group",
"com.apple.DevToolsNonRelocatableShared.pkg-group"
);
PackageIdentifier = "com.apple.pkg.DeveloperToolsCLI";
PackageVersion = "4.5.0.0.1.1249367152";
PathACLs = {
Library = "!#acl 1\\ngroup:ABCDEFAB-CDEF-ABCD-EFAB-CDEF0000000C:everyone:12:deny:delete\\n";
System = "!#acl 1\\ngroup:ABCDEFAB-CDEF-ABCD-EFAB-CDEF0000000C:everyone:12:deny:delete\\n";
};
}
