What part of this regex is not supported by json schema and can it be rewritten to support it?

Question

Apparently json schema doesn't like this regex: ^(?=.{1,63}$)([-a-z0-9]*[a-z0-9])?$

I get an error: pattern must be a valid regex. This error means the regex pattern I'm using is invalid according to json schema.

My regex seems to be valid for most other parsers though. and json schema supports positive and negative look aheads and capture groups: https://json-schema.org/understanding-json-schema/reference/regular_expressions.html

Is there some json schema specific escaping I need to do with my pattern?

I'm at a loss to see what it doesn't like about my regex.

The regex I want will do the following:

Allow lower case chars, numbers and "-"
Can start with but not end with "-"
Max length of string cannot exceed 63 chars

You don't really need the lookahead and the capture group, and it does not have to be optional as well. Try ^[-a-z0-9]{0,62}[a-z0-9]$ regex101.com/r/LCsubB/1 — The fourth bird
– The fourth bird, Commented Jan 4, 2022 at 20:20
Please make that an answer and I will mark as correct. Tested and confirmed it works for me and json schema doesn't complain about it. — red888
– red888, Commented Jan 4, 2022 at 20:23
Glad it works for you. I posted an answer, but why your pattern does not work I am not sure. Perhaps another answer will be posted that can explain the reason. — The fourth bird
– The fourth bird, Commented Jan 4, 2022 at 20:26
Please also note that RegEx support is very much an implementation-level thing since not all platforms fully support ECMA 262. — gregsdennis
– gregsdennis, Commented Jan 4, 2022 at 21:40
"the regex pattern I'm using is invalid according to json schema" - what implementation are you using? have you checked its documentation to see if there are any limitations in its regex support? have you filed a bug report? — Ether
– Ether, Commented Jan 4, 2022 at 23:46

The fourth bird · Accepted Answer · 2022-01-04 20:24:59Z

2

You could simplify the pattern to use the character classes and quantifiers without using the lookahead and the capture group.

You can change the quantifiers, matching 0-62 chars allowing the - and a single char without the - as a single char would also mean that it is at the end.

^[-a-z0-9]{0,62}[a-z0-9]$

Regex demo

answered Jan 4, 2022 at 20:24

The fourth bird

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