REGEX a-z 0-9 but not only numbers

Question

Trying to match only strings 10-30 characters long with only a-z and 0-9 (but not only numbers) in the string. Seems to work Except when the string starts with a number then it fails. Not sure about the \D which should fix the not only numbers

static final Pattern UNIQUE_ID_PATTERN = Pattern.compile("^\\D[A-Za-z0-9_-]{10,30}$");
UNIQUE_ID_PATTERN.matcher("1eeeeeeeee333e").matches(); // Does not work
UNIQUE_ID_PATTERN.matcher("eeeeeeeee333e").matches(); // Works

Wiktor Stribiżew · Accepted Answer · 2015-08-28T14:48:53.267

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The \D shorthand class means any non-digit symbol. You should remove it from the pattern (so that it becomes "^[A-Za-z0-9_-]{10,30}$") for the matches to return true, as 1 is a digit in 1eeeeeeeee333e.

If you want to place a restriction (the string cannot consist of only digits) use an anchored look-ahead:

^(?![0-9]+$)[A-Za-z0-9_-]{10,30}$

Here is a demo

Or, a shortened version with i modifier making the pattern case-insensitive:

(?i)^(?![0-9]+$)[A-Z0-9_-]{10,30}$

edited Aug 28 '15 at 14:48

answered Aug 28 '15 at 08:04

Wiktor Stribiżew

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I updated the answer with a version to disallow digit-only strings. – Wiktor Stribiżew Aug 28 '15 at 08:05
Nice. +1 for the negative look ahead. – xyz Aug 28 '15 at 08:11
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I suggest that you read [*Various Uses for Lookarounds* at rexegg.com](http://www.rexegg.com/regex-lookarounds.html#uses). It is quite useful. – Wiktor Stribiżew Aug 28 '15 at 08:16
it does not work for me. – SalahAdDin Sep 23 '22 at 13:49
@SalahAdDin Then your issue is different from the OP. – Wiktor Stribiżew Sep 23 '22 at 13:50
the next answer worked for me. – SalahAdDin Sep 23 '22 at 13:50
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@SalahAdDin The OP problem is *not matching a string that only contains digits*. The [next answer](https://stackoverflow.com/a/32267206/3832970) shows how to match a string that *must contain at least one ASCII letter*, and is a solution, too, but uses different logic. – Wiktor Stribiżew Sep 23 '22 at 13:53

score 2 · Answer 2 · edited May 23 '17 at 11:43

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Another way: ^(?=(?:.*[a-zA-Z])+)([a-zA-Z\d]{10,30})$ update

Demo

More details

edited May 23 '17 at 11:43

Community

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answered Aug 28 '15 at 09:01

Ahosan Karim Asik

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This is not JavaScript, see the post tags. In Java, you cannot use regex delimiters as in JavaScript or PHP. – Wiktor Stribiżew Aug 28 '15 at 14:48

REGEX a-z 0-9 but not only numbers

2 Answers2