re = /^\S+(?=.*?Samsung_Galaxy_Note_2)/m
str = 'List of devices attached
192.168.56.101:5555 device product:vbox86p model:Samsung_Galaxy_Note_2___4_3___API_18___720x1280 device:vbox86p
192.168.56.102:5555 device product:vbox86tp model:Google_Nexus_7___4_3___API_18___800x1280 device:vbox86tp'
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