re = /(?<!XXY)(?<=Y)\w(?=Y)(?!YYXX)/m
str = '(?<!XXY)(?<=Y)\\w(?=Y)(?!YYXX)
^ ^ ^ ^ ^
| | | | not before YYXX
| | |before Y
| |letter
| followed by Y
not followed by XXY
X0XYXYYX
X(?=Y) match X if before Y
X(?!Y) match X if not before Y
(?<=Y)X match X if followed by Y
(?<!Y)X match X if not followed by Y'
# Print the match result
str.scan(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