re = /.*?id="(.*?)".*?time">(.*?)<\/.*?subject">\[(.*?)\].*?|.*$/
str = '<div class="list" id="1">
<div class="time">12:01 PM</div>
<div class="subject">[This is dummy Subject1] This is some dummy strings after subject</div>
<div/>
<div class="list" id="2">
<div class="time">12:01 PM</div>
<div class="subject">[This is dummy Subject2] This is some dummy strings after subject</div>
<div/>
<div class="list" id="3">
<div class="time">12:01 PM</div>
<div class="subject">[This is dummy Subject3] This is some dummy strings after subject</div>
<div/>'
subst = '$1|$2|$3\\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