Regular Expressions 101

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/
^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=.\-_*])([a-zA-Z0-9@#$%^&+=*.\-_]){3,}$
/
^ asserts position at start of the string
Positive Lookahead
(?=.*[0-9])
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 present in the list below
[0-9]
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (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 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
(?=.*[@#$%^&+=.\-_*])
Assert that the Regex below matches
.
matches any character (except for line terminators)
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Match a single character present in the list below
[@#$%^&+=.\-_*]
@#$%^&+=.
matches a single character in the list @#$%^&+=. (case sensitive)
\- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
_*
matches a single character in the list _* (case sensitive)
1st Capturing Group
([a-zA-Z0-9@#$%^&+=*.\-_]){3,}
{3,} matches the previous token between 3 and unlimited times, as many times as possible, giving back as needed (greedy)
A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data
Match a single character present in the list below
[a-zA-Z0-9@#$%^&+=*.\-_]
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)
@#$%^&+=*.
matches a single character in the list @#$%^&+=*. (case sensitive)
\- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
_ matches the character _ with index 9510 (5F16 or 1378) literally (case sensitive)
$ asserts position at the end of the string
Your regular expression does not match the subject string.

Regular Expression
No Match

/
/

Test String