Regular Expression advice for [Alphanumeric][alphanumeric.-_@] 31 characters

Question

I'm looking to do a name check using regex in javascript.

1. The value can contain alphanumeric and following special characters ('-', '.' '_' and '@').
2. It should always start with an alphanumeric character.
3. It should not be an empty string.
4. Maximum allowed length for this parameter is 31 characters.
5. This parameter is case-insensitive.

I came up with this, but feel it's incorrect. Any advice on how to have it foolproof?

^[A-Za-z0-9]+[A-Za-z0-9_@-.]{30}

Answer 1

You are quite close, here is the corrected regex:

/^[a-z0-9][\w@.-]{0,30}$/i

I applied the folloing changes:

• Added $ anchor to the end
• used the i-modifier for case-insensitivity
• replaced a-zA-Z0-9_ with \\w and moved - to the end of the character class
• changed fixed repetition {30} to {0,30}

See the Regex101-Demo with some unit tests.

Answer 2

^[A-Za-z0-9][A-Za-z0-9_@.-]{0,30}

• place - at the and of brackets, so it won't be used as a range
• allow 1-31 characters {,30}
• remove + after first character (without it you would get >31 chars)

Answer 3

You can always check your patterns at www.regexr.com

• You need to escape the '-' with and backslash like this: \\- .
• You need to remove the + in the middle part
• Change {30} to {0,30} because it doesn't need to be exactly 31 characters long
• Add \\i to the end for case insensitive and remove the AZ parts
• Close the pattern with $

Result looks like this:

/[a-z0-9][a-z0-9@\-._]{0,30}/i