re = /\/(\d+)_.*$/
str = 'http://userimages-akm.imvu.com/catalog/includes/modules/phpbb2/images/avatars/145870556_47076915459092eafd7b69.jpg'
# Print the match result
str.match(re) do |match|
puts match.to_s
end
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