Create a Gemfile with the specified gems.

gemfile.sh

#!/bin/bash

# Usage:
#
# $ gemfile sinatra
# $ cat Gemfile
# source 'https://rubygems.org'
# gem 'sinatra'

function gemfile {
  echo "source 'https://rubygems.org'" > './Gemfile'
  for var in "$@"
    do
      echo "gem '"$var"'" >> './Gemfile'
    done
}