re = /<img.+?src=[\"'](.+?)[\"']>/
str = 'Lorem ipsum dolor sit amet <img src="https://pbs.twimg.com/profile_images/1075946974354886657/q-CYuf8L.jpg"> Sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus<img src="https://pbs.twimg.com/profile_images/1075946974354886657/q-CYuf8L.jpg">.
'
subst = 'ciao'
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