You don't have write permissions for the *** directory.

% gem install cucumber
You don't have write permissions for the /usr/bin directory.

If you meet the error when you install something on CLI, you should execute below command.

// Change ownership

% sudo chown -R $USER /usr/bin


// Reinstall

% gem install cucumber
Successfully installed diff-lcs-1.2.5
Fetching: multi_test-0.1.2.gem (100%)
Successfully installed multi_test-0.1.2
Fetching: cucumber-2.0.0.gem (100%)
Successfully installed cucumber-2.0.0
Parsing documentation for diff-lcs-1.2.5
Installing ri documentation for diff-lcs-1.2.5
Parsing documentation for multi_test-0.1.2
Installing ri documentation for multi_test-0.1.2
Parsing documentation for cucumber-2.0.0
Installing ri documentation for cucumber-2.0.0
3 gems installed

Success.