How to match a string with at least one letter, allowing only certain characters?

Question

I am writing a regular expression which matches a string with the following conditions. if the string does not match, it will prevent the user from typing(in a UI textbox).

must have at least one alphabet
may start or end with "',-
must not have spaces at the start or end
may contain numbers
may have space in the middle of the string

This is what I have so far. but it allows the text to end with a space.

^["',-]*[a-zA-Z][a-zA-Z0-9"',\ ]*[a-zA-Z0-9"']$

you are right. its bit hard to factor in everything. I am thinking hard as I can. — Arun Kamalanathan, Aug 25 '21 at 09:32
Btw, you can scratch rules 5,6 & 8. It's all covered by the 1st one. Whilst the 3rd one also covered the 7th one. — JvdV, Aug 25 '21 at 09:49

score 1 · Accepted Answer · answered Aug 25 '21 at 09:27

1

You may use the following pattern:

^(?! |.* $)(?=.*[a-zA-Z])[a-zA-Z0-9"',\ \-]+$

Demo.

Breakdown:

^ - Beginning of string.
(?! |.* $) - Negative Lookahead: doesn't start or end with a space.
(?=.*[a-zA-Z]) - Positive Lookahead: contains at least one letter.
[a-zA-Z0-9"',\ \-]+ - Match one or more characters including letters, digits, ", ', -, and a space character.
$ - End of string.

answered Aug 25 '21 at 09:27

41686d6564 stands w. Palestine

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it should not allow space in the middle – Arun Kamalanathan Aug 25 '21 at 09:30
1

@ArunK That contradicts the rules in the question which says _"must **not** have spaces at the **start or end**"_ and _"**may have** space in the **middle** of the string"_. Which one is correct? – 41686d6564 stands w. Palestine Aug 25 '21 at 09:31
yes sorry. ignore that. I didnt want space between numbers "1 2" . but your regex is covering it too – Arun Kamalanathan Aug 25 '21 at 09:33
@ArunK It will not accept `1 2` but _will_ accept `a 1 2` or `1 2a`, for example. You need to make up your mind about the rules. – 41686d6564 stands w. Palestine Aug 25 '21 at 09:35
@ArunK See [this](https://www.regular-expressions.info/lookaround.html) and [this](https://stackoverflow.com/a/2973495/8967612). – 41686d6564 stands w. Palestine Aug 25 '21 at 09:41
thanks so much. I have a question, is it also possible to check whether the maximum string length doesn't exceed 6 characters. I can do this at the application level. Just wanted to see if its possible with regex. – Arun Kamalanathan Aug 25 '21 at 09:44
Sure, you can either add another Lookahead at the beginning (`(?=.{1,6}$)`) or add another alternation to the existing negative Lookahead (i.e., `(?! |.* $|.{7})`). Good luck :) – 41686d6564 stands w. Palestine Aug 25 '21 at 09:52

How to match a string with at least one letter, allowing only certain characters?

1 Answers1