.NET Regular Expression Anchors

Question

This is a question about the answer asked in the question Check the line to see if all characters are hexadecimal values .

The suggested regular expression is as follows:

\A\b[0-9a-fA-F]+\b\Z 

Now \A and \Z seem equivalent to ^ and $ respectively. \Z behaves differently because it allows you to use a new line after it (it may or may not be intended).

I don’t understand why the anchor \b "match at word boundary" is used. Isn't the beginning / end of a line always a word boundary?

Ultimately, the regular expression can be rewritten as ^[0-9a-fA-F]$ with the same behavior (without taking into account the problem of returning \n ). Am I missing something? Is \b for some weird edge?

Test cases:

 123ABC -> true 123def -> Returns true 123g -> Returns false 

Answer 1

the boundary of the word \b corresponds to characters without a word and a word, and also at the beginning of a line if the first character is a word character, and at the end if the last character is a word character.

Thus, \A\b[0-9a-fA-F]+\b\Z is equal to \A[0-9a-fA-F]+\Z , because all characters in the string must be characters of the word ( [0-9] digits or [a-fA-F] letters) to match the pattern.

In this case, there will be another story: \A\b[0-9a-fA-F-]+\b\Z , which will correspond only to lines with the word characters at the beginning and end.

Use \z to match the whole string, without permission \n at the end.