Ruby Mechanize Script fails on PHP execution, but works on SSH with Putty

Question

I am trying to run a Ruby script that scrapes some URL, and execute it from PHP.

This is my PHP code:

PHP:

$url = 'https://www.example.com';

$result= shell_exec("ruby script.rb $url");

echo 'result is:';

echo $result;

I have two different codes, one is based on Curl, and it works:

Working Ruby Code:

value = `curl #{ARGV[0]} | grep "findMe:"`
result = value.scan(/findMe: (.*)/).flatten.first.split('$').last.gsub(',', '').to_f
puts result

But the other one is using mechanize gem, and it doesn't work from PHP:

None Working Code:

require 'time'
require 'mechanize'

url = ARGV.first

begin
  page = Mechanize.new.get(url).content
  result = page.match(/findMe: "\$(.+)"/)[1].tr(',', '')

  # Uncomment following line to see date and time in output
  # output = Time.now.strftime('[%F %T %z] ') + result

  # Uncomment following line to see only result in output
  output = result

  # Output the result on terminal
  puts result

rescue => detail
  puts detail.message
end

But, from SSH, using Putty, both Ruby scripts work perfect.

So how could it be that one of them is failing on PHP execution?

Update:

As I was advised, I changed shell to:

$result = `ruby script.rb "$url" 2>&1`;

This is the error:

result is:script.rb:2:in `require': no such file to load -- mechanize (LoadError) from script.rb:2

Maybe it does have to do with paths, but I'm not sure how to change them correctly