# cheatsheet

tiny regex cheatsheet

expr usage
/hello/ looks for the string between the forward slashes (case-sensitive)
/hello/i looks for the string between the forward slashes (case-insensitive)
/hello/g looks for multiple occurrences of string between the forward slashes
/h.llo/ the '.' matches any one character other than a new line character... matches 'hello', 'hallo' but not 'h
llo'
/h.*llo/ the "*" matches any character(s) zero or more times... matches "hello", "heeeeeello", "hllo", "hwarwareallo"
/\d/ matches any digit
/\D/ matches any non-digit
/\w/ matches any word character (a-z, A-Z, 0-9, _)
/\W/ matches any non-word character
/\s/ matches any white space character (\r (carriage return),\n (new line), \t (tab), \f (form feed))
/\S/ matches any non-white space character
/[abcd]/ matches any character in square brackets
/[ch]at/ matches cat or hat
/[^abcd]/ matches anything except the characters in square brackets
/[a-z]/ matches all lowercase letters (a to z)
/[A-Z]/ matches all uppercase letters (A to Z)
/[0-9]/ matches all digits
/[a-zA-Z]/ matches all lowercase and uppercase letters
/[^a-zA-Z]/ matches non-letters
/[a-zA-Z0-9]/ matches all lowercase, uppercase letters and numbers
/(hello){4}/ matches "hellohellohellohello"
/hello{3}/ matches "hellooo" and "helloooo" but not "helloo"
/(hello){1,3}/ matches "hello" that occur between 1 and 3 times (inclusive)
/(hello){3,}/ matches "hello" that occur atleast 3 times
/ab*c/ matches zero or more repetitions of "b" (matches "abc", "abbbbc", "ac")
/ab+c/ matches one or more repetitions of "b" (matches "abc", "abbbbc", but not "ac")
/^/ matches beginning of a line
/$/ matches end of a line
/(hard)?work/ matches "work" or "hardwork"
/(?:hard)?work/ matches "work" or "hardwork" but is a non-capturing group
/i am a (cat|dog|whale) person/ matches "i am a cat person", "i am a dog person" and "i am a whale person"
/z(?=a)/ positive lookahead... matches the "z" before the "a" in pizza but not the first "z"
/z(?!a)/ negative lookahead... matches the first "z" but not the "z" before the "a"
/(?<=[aeiou])\w/ positive lookbehind... matches any word character that is preceded by a vowel
/(?<![aeiou])\w/ negative lookbehind... matches any word character that is not preceded by a vowel
iHateRegex
by geon

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