Regex Cheatsheet

? is used for string that is optionally present
/colou?r/matches "color" and "colour"
/color|colour/matches either, just like previous example
/[a-z]*/matches zero or more alphabet chars
/[a-z]+/matches one or more alpha chars
/[^0-9]/matches strings with NO digits
/^[0-9]/matches strings that START with a digit
/[0-9]{1}/matches a single digit
/[0-9]{1,}/matches one digit or more
/[0-9]{2,4}/matches 2,3 or 4 digits
/[0-9]{2}-[0-9]{2}-[0-9]{2,4}/matches dates like mm-dd-yy and mm-dd-yyyy
/[\d]{2}-[\d]{2}-[\d]{2,4}/this is same as previous, but using \d which matches digit chars
/\b[\d]/- matches initial word boundary, via \b, which matches a digit, ex: "4chan"
/[\d]\b/- matches digit at final word boundary, like "fab4"
/\S+@\S+?/- matches abc@def" using \S which matches non-whitespace chars

back reference: we use \1 to match one more instance of whatever was matched in ()/([a-z]+) +\1/
literals can be denoted by using backslashes, like to search for period or question mark: /127\.0\.0\.1/ or /who\?/
dates, example format: mm/dd/yyyy /^(0[1-9]|1[0-2])\/(0[1-9]|[12][0-9]|3[0-1])\/([12][0-9]{3})$/
times with hour:min and optional am/pm/^(1[0-2]|0?[1-9]):([0-5]?[0-9]) ( ?[AaPp][Mm])?$/
IP address ex: n.n.n.n where 0 <= n <= 255, ignoring some invalid IP matches like 0.0.0.0 /^([0-9]{1,3}\.){3}([0-9]{1,3})$/
simple URL matching protocol://domain.ext /^(https?|s?ftp|file)://.+\.[a-z]{2,}$/
case sensitive match: ?i, ex: match THE or the or The - /the/i
positive lookahead match: ?= ex: match passwords with length of 8-12 chars and upper, lower and numeric chars like abC1 or A2bc or 9rE9 - /^(?=.{8,12})(?=.*[a-z])(?=.*[A-Z])(?=.*[0-9]).*/

Mike's Regex Cheatsheet