re = /(?:<FONT[^>]*>|<\/FONT>)/m
str = '<UL><LI><FONT size=2 face=Verdana>random text<STRONG>random text</STRONG>random text<SPAN style="LINE-HEIGHT: 115%; FONT-FAMILY: \'Arial\',\'sans-serif\'; FONT-SIZE: 11pt; mso-fareast-font-family: \'Times New Roman\'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA"><SPAN style="mso-spacerun: yes"> </SPAN>random text</SPAN> </FONT></LI> <LI><FONT size=2 face=Verdana><FONT size=2 face=Verdana><STRONG>random text</STRONG></FONT></LI> <LI>random text</FONT></LI> <LI><FONT size=2 face=Verdana>random text</FONT></LI> <LI><FONT size=2 face=Verdana>random text</FONT></LI'
subst = ''
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