Execute Ruby gem in Objective-C fails with NSTask

Question

I'm trying to run a Ruby gem called Cupertino (https://github.com/nomad/cupertino) from an Objective-C app. The ios login command works fine from the terminal.

When I try to run it using an NSTask, I get the following error:

/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in require': cannot load such file -- commander/import (LoadError) from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in require' from /Users/Ben/.rvm/gems/ruby-2.1.0/gems/cupertino-0.9.5/bin/ios:3:in `'

If I try to install the gem using rbenv instead of rvm, I get this error instead:

/Library/Ruby/Gems/2.0.0/gems/commander-4.1.5/lib/commander/runner.rb:365:in block in require_program': program version required (Commander::Runner::CommandError) from /Library/Ruby/Gems/2.0.0/gems/commander-4.1.5/lib/commander/runner.rb:364:in each' from /Library/Ruby/Gems/2.0.0/gems/commander-4.1.5/lib/commander/runner.rb:364:in require_program' from /Library/Ruby/Gems/2.0.0/gems/commander-4.1.5/lib/commander/runner.rb:52:in run!' from /Library/Ruby/Gems/2.0.0/gems/commander-4.1.5/lib/commander/delegates.rb:7:in run!' from /Library/Ruby/Gems/2.0.0/gems/commander-4.1.5/lib/commander/import.rb:10:in block in ' /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in require': cannot load such file -- cupertino (LoadError) from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in require' from /Users/Ben/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/cupertino-0.9.5/bin/ios:7:in `'

This is the method I am using:

- (void)login {
    NSTask* task = [[NSTask alloc] init];
    [task setLaunchPath:@"/Users/Ben/.rvm/gems/ruby-2.1.0/gems/cupertino-0.9.5/bin/ios"];
    [task setArguments:@[@"login"]];

    NSPipe *pipe;
    pipe = [NSPipe pipe];
    [task setStandardOutput: pipe];

    NSFileHandle *file;
    file = [pipe fileHandleForReading];

    [task launch];

    NSData *data;
    data = [file readDataToEndOfFile];

    NSString *string;
    string = [[NSString alloc] initWithData: data encoding: NSUTF8StringEncoding];
    NSLog(@"task output: %@",string);

    [task waitUntilExit];
}

I'm a bit lost - this seems to be some sort of clash between the system version of Ruby and my version. Any ideas on how I can get this up and running?