Ruby: How to REQUIRE an installed GEM programmatically?

Question

First off, I am REALLY new at coding, only CMD 10 years ago and ruby for 5 days now. So I am making my very first script and the only goal for it is for me to test and learn DEF and TRUE/FALSE choices

Like like this:

def cls
    system "clear" or "cls"
end

or

def s2
    sleep 2
end

My question:

I want my script to check if a particular GEM is installed, so i made the code. but i cant figure out how to make the script REQUIRE the particular Gem IF installed. or make the script INSTALL a Gem IF not installed OR at least say "sorry no GEM, EXIT" and then end script.

def checkGemColorize(gemName, versionLimit=nil)
isAvailable = false
begin
    if versionLimit == nil
        gem  gemName
       puts "Yes the GEM is installed"
#the script should put in require 'colorize' if installed
   else
     gem  gemName, versionLimit
       puts "Yes the GEM is installed with correct version number"
#also if version number is used.
    end
    isAvailable = true
rescue LoadError
end
isAvailable
end
sleep 0.5
#testing IF TRUE on colorize
puts "checking for colorize GEM"
  sleep 0.5
puts checkGemColorize('colorize')
  sleep 1
#testing IF TRUE version number
puts "checking for colorize version number"
  sleep 0.5
puts checkGemColorize('colorize', '>=0.6')
  sleep 1
#testing IF FALSE version number is shown when input is higher
puts "checking false version number"
  sleep 0.5
puts checkGemColorize('colorize', '>=1.2')
  sleep 1
#testing IF FALSE parameter
puts "a fake gem for testing FALSE"
  sleep 0.5
puts checkGemColorize('not_colorize')
  sleep 1
puts "testing"
  sleep 1
puts "test".red

This is the working code thanks to K M Rakibul Islam

def checkGemColorize(gemName, versionLimit=nil)
  isAvailable = false
  begin
    if versionLimit == nil
      gem_present = gem  gemName # this will return true if the gem is present
      if gem_present
        puts "Yes the GEM is installed"
        require gemName # here you are requiring the gem
        puts "#{gemName} GEM is required just now"
      end
    else
      gem  gemName, versionLimit
      puts "Yes the GEM is installed with correct version number"
#also if version number is used.
    end
    isAvailable = true
  rescue LoadError
    # I added this block of code to install the gem when it's missing
    puts "#{gemName} is missing, Installing now...."
    `gem install #{gemName}` # installing the missing gem
    puts "installed the #{gemName} gem just now!"
    isAvailable = true
  end
  isAvailable
end

Answer 1

You can require the gem if it's present and also install the gem if it's not already installed the following way (Look for the comments in the code):

def checkGemColorize(gemName, versionLimit=nil)
  isAvailable = false
  begin
    if versionLimit == nil
      gem_present = gem  gemName # this will return true if the gem is present
      if gem_present
        puts "Yes the GEM is installed"
        require gemName # here you are requiring the gem
        puts "#{gemName} GEM is required just now"
      end
    else
      gem  gemName, versionLimit
      puts "Yes the GEM is installed with correct version number"
#also if version number is used.
    end
    isAvailable = true
  rescue LoadError
    # I added this block of code to install the gem when it's missing
    puts "#{gemName} is missing, Installing now...."
    `gem install #{gemName}` # installing the missing gem
    puts "installed the #{gemName} gem just now!"
    isAvailable = true
  end
  isAvailable
end

#testing IF TRUE on colorize
puts "checking for colorize GEM"
puts checkGemColorize('colorize')