“rails new” Not creating a new application

“rails new” Not creating a new application

I tried to make a new Rails app when I got this error.

   Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    current directory: /Users/stefan/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/nio4r-2.3.1/ext/nio4r
/Users/stefan/.rbenv/versions/2.4.0/bin/ruby -r ./siteconf20190212-24856-1bhk2ja.rb extconf.rb
checking for unistd.h... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
    --with-opt-dir
    --without-opt-dir
    --with-opt-include
    --without-opt-include=${opt-dir}/include
    --with-opt-lib
    --without-opt-lib=${opt-dir}/lib
    --with-make-prog
    --without-make-prog
    --srcdir=.
    --curdir
    --ruby=/Users/stefan/.rbenv/versions/2.4.0/bin/$(RUBY_BASE_NAME)
/Users/stefan/.rbenv/versions/2.4.0/lib/ruby/2.4.0/mkmf.rb:457:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
    from /Users/stefan/.rbenv/versions/2.4.0/lib/ruby/2.4.0/mkmf.rb:588:in `try_cpp'
    from /Users/stefan/.rbenv/versions/2.4.0/lib/ruby/2.4.0/mkmf.rb:1095:in `block in have_header'
    from /Users/stefan/.rbenv/versions/2.4.0/lib/ruby/2.4.0/mkmf.rb:945:in `block in checking_for'
    from /Users/stefan/.rbenv/versions/2.4.0/lib/ruby/2.4.0/mkmf.rb:351:in `block (2 levels) in postpone'
    from /Users/stefan/.rbenv/versions/2.4.0/lib/ruby/2.4.0/mkmf.rb:321:in `open'
    from /Users/stefan/.rbenv/versions/2.4.0/lib/ruby/2.4.0/mkmf.rb:351:in `block in postpone'
    from /Users/stefan/.rbenv/versions/2.4.0/lib/ruby/2.4.0/mkmf.rb:321:in `open'
    from /Users/stefan/.rbenv/versions/2.4.0/lib/ruby/2.4.0/mkmf.rb:347:in `postpone'
    from /Users/stefan/.rbenv/versions/2.4.0/lib/ruby/2.4.0/mkmf.rb:944:in `checking_for'
    from /Users/stefan/.rbenv/versions/2.4.0/lib/ruby/2.4.0/mkmf.rb:1094:in `have_header'
    from extconf.rb:14:in `<main>'

To see why this extension failed to compile, please check the mkmf.log which can be found here:

  /Users/stefan/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/extensions/x86_64-darwin-16/2.4.0-static/nio4r-2.3.1/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /Users/stefan/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/nio4r-2.3.1 for inspection.
Results logged to /Users/stefan/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/extensions/x86_64-darwin-16/2.4.0-static/nio4r-2.3.1/gem_make.out

An error occurred while installing nio4r (2.3.1), and Bundler cannot continue.
Make sure that `gem install nio4r -v '2.3.1'` succeeds before bundling.
         run  bundle exec spring binstub --all
Could not find gem 'puma (~> 3.11)' in any of the gem sources listed in your Gemfile.
Run `bundle install` to install missing gems.

I tried to make a new Rails app when I got this error.

I ran rails new portfolio to start a new portfolio project for myself. Could someone please help me with this error?

Not sure what to look for in the error message above.

I am using macOS 10.14.2 if it helps

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