re = /^(.+?) ?\b(\d{4})\b(.*?)$/im
str = 'Visiting relatives 2010
2017 trip
Old photos from 2001
Old 2002 photos
'
subst = '$2 $1$3'
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