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I have defined a regular expression of hexadecimal value of length 4 as follows:
([0-9A-F]{4})
And it works fine and grammatically
0000
is also a valid hexadecimal number , but I want to discard it from the valid matching and therefore looking forward to hint on how to extend the current regular expression so that
0000 is flagged as invalid and filtered out.
Thanks
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'?' matches/verifies the zero or single occurrence of the group preceding it. Check Mobile number example. Same goes with '*' . It will check zero or more occurrences of group preceding it.
\$ will help to find the character "$" available in the content based on the expression flags assigned to the regular expression.
Yes, in hexadecimal, things like A, B, C, D, E, and F are considered numbers, not letters. That means that 200 is a perfectly valid hexadecimal number just as much as 2FA is also a valid hex number.
A regular expression (shortened as regex or regexp; sometimes referred to as rational expression) is a sequence of characters that specifies a search pattern in text. Usually such patterns are used by string-searching algorithms for "find" or "find and replace" operations on strings, or for input validation.
You could use negative lookahead:
(?!0000)[0-9A-F]{4}
Here (?!0000) is a negative lookahead group. It more or less says: "And do not allow that the next elements are 0000" but without consuming them.
You can test it on regex101.
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