c# - Regex to allow only these [A-Z] / [a-z] / [0-9] / "-" / "." / "_" / "~"

Question

Closed. This question is not reproducible or was caused by typos. It is not currently accepting answers. question from:https://stackoverflow.com/questions/65897009/regex-to-allow-only-these-a-z-a-z-0-9

Answer 1

Your expression is as follows:

^[a-zA-Z0-9~-_.]S{42,128}$

Let's break it down into its components:

• ^ - Matches the beginning of the input.
• [a-zA-Z0-9~-_.] - Match a single character a-z A-Z 0-9 ~ - _ or .
• S - Matches any character except a white-space character.
• {42,128} - Matches previous element at least 42 times and at most 128 times. In this case, the previous element is S.
• $ - Matches the end of the input, or the point before a final at the end of the input.

Source for most definitions

So as we can see your regular expression currently does the following:

It first matches a single character a-z A-Z 0-9 ~ - _ or . at the start of the string. It then matches any non-whitespace character 42-128 times, and expects the end of the input to follow immediately afterwards. This means that we expect a string with a total length of 43-129 characters.

As your question states, you only want to match those specific characters, so your expression should actually be this (I've removed the S):

^[a-zA-Z0-9~-_.]{42,128}$

As for your specific input:

longenoughlongenoughlongenoughlongenoughlongenoughlongenoughlongenoughlongenoughAABSC__-......~~~.~-!

It appears that you have included an exclamation mark (!) at the end of your input, which of course doesn't match your constraint.