I am trying to find out a regex pattern to check if a password contains at least: one lowercase letter, one uppercase letter, one numeric digit, and one special character(Symbol)
I came across this regex: ^(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[^a-zA-Z0-9])(?!.*\s) but I don't really understand well what each part is doing, If someone has a bit of free time I would be very thankful if you could explain to me what each part does.
If you paste it into https://regex101.com/ you get this explanation. I suggest you use this site to experiment and understand. Also the explanation is formatted in a much better way
If you want to learn regex you need to start with something simpler
^ asserts position at start of a line Positive Lookahead (?=.
*\d) Assert that the Regex below matches . matches any character (except for line terminators)*matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy) \d matches a digit (equivalent to [0-9]) Positive Lookahead (?=.*[a-z]) Assert that the Regex below matches . matches any character (except for line terminators)*matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy) Match a single character present in the list below [a-z] a-z matches a single character in the range between a (index 97) and z (index 122) (case sensitive) Positive Lookahead (?=.*[A-Z]) Assert that the Regex below matches . matches any character (except for line terminators)*matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy) Match a single character present in the list below [A-Z] A-Z matches a single character in the range between A (index 65) and Z (index 90) (case sensitive) Positive Lookahead (?=.*[^a-zA-Z0-9]) Assert that the Regex below matches . matches any character (except for line terminators)*matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy) Match a single character not present in the list below [^a-zA-Z0-9] a-z matches a single character in the range between a (index 97) and z (index 122) (case sensitive) A-Z matches a single character in the range between A (index 65) and Z (index 90) (case sensitive) 0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive) Negative Lookahead (?!.*\s) Assert that the Regex below does not match . matches any character (except for line terminators)*matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy) \s matches any whitespace character (equivalent to [\r\n\t\f\v ]) Global pattern flags g modifier: global. All matches (don't return after first match) m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
Your regex pattern contains a number of positive lookahead assertions, which are checking for the presence of various things in the input. Here is an explanation:
^ from the start of the input
(?=.*\d) assert one or more digits are present
(?=.*[a-z]) assert lowercase letters
(?=.*[A-Z]) assert uppercase letters
(?=.*[^a-zA-Z0-9]) assert one or more characters which are NOT alphanumeric
(?!.*\s) assert one or more whitespace characters
You can google the regular expression cheat sheet to have an understanding of it. Here is one that I found useful, https://cheatography.com/davechild/cheat-sheets/regular-expressions/
You can also look at https://regex101.com/ and play around with regex.
