re = /\s*<script src="\/((\w+)[\w.\/]+)"><\/script>/
str = '<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="Content-Security-Policy" content="default-src * data: gap: https://ssl.gstatic.com; style-src * \'unsafe-inline\'; script-src * \'unsafe-inline\' \'unsafe-eval\'">
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<title>atomic-project</title>
</head>
<body>
<div id="app"></div>
<!-- built files will be auto injected -->
<script src="/app.js"></script><script src="/app.js"></script><script src="/app.js"></script><script src="/app.js"></script></body>
</html>
'
subst = '\\n<script>\\n const $2Script = document.createElement(\'script\');\\n $2Script.type = \'text/javascript\';\\n $2Script.async = true;\\n $2Script.src = \'$1\';\\n document.body.appendChild($2Script);\\n</script>\\n'
result = str.gsub(re, subst)
# Print the result of the substitution
puts result
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Ruby, please visit: http://ruby-doc.org/core-2.2.0/Regexp.html