I am trying to create a javascript regex for below conditions Allow Alphanumeric only But also allow underscore(_) Don't allow to start with a number Don't allow to start with an underscore I have created a regex ^(?![0-9]|[_].*$).* which will work for last two conditions above. Please suggest how can I add an and condition to make it work for all above scenarios.

You may use the following regex: ^[A-Za-z]\w*$ Details ^ - start of string [A-Za-z] - any ASCII letter \w* - zero or more letters/digits/ _ $ - end of string. To allow an empty string match, wrap the whole pattern with an optional non-capturing group: ^(?:[A-Za-z]\w*)?$ ^^^ ^^

javascriptregex

Prashobh

Reputation: 9544

Regex for a string which do not start with a number and allow only alphanumeric

I am trying to create a javascript regex for below conditions

Allow Alphanumeric only
But also allow underscore(_)
Don't allow to start with a number
Don't allow to start with an underscore

I have created a regex ^(?![0-9]|[_].*$).* which will work for last two conditions above. Please suggest how can I add an and condition to make it work for all above scenarios.

Upvotes: 5

Answers (4)

Caius Jard

Reputation: 74710

You may be thinking too literally about the last two requirements. If it's alphanumeric (so.. a-z and 0-9, right?) then saying "dont allow numbers or underscore at the start" is probably the same as "must start with a letter"

^[a-z][a-z0-9_]*$

This is "must start with a-z", followed by "must follow with zero or more letters, numbers or underscores. The ^ outside of a character class (for example [a-z] is a character class) means "start of input". The $ means end of input.

If you interpreted the last two requirements literally, you could write:

[^0-9_]

This means "any character that is not 0-9 and also not an underscore" but it doesn't necessarily restrict the user from entering something other than a-z as the first character, so they might enter a #, and it would pass..

Upvotes: 3