Regex not accepting single character

Question

I am using following regex to have validation like

• String should not start with space

• String should be alpha numeric with space, hyphen and underscore in them

  [^-\s][a-zA-Z0-9_\s-]+$

Debuggex Demo

But this is NOT accepting single character input. Can anyone please help me to achieve the same validation and also accept a single character alpha numeric?

Answer 1

The regex [^-\s][a-zA-Z0-9_\s-]+$ is looking for:

• One character that is not a hyphen or space; then
• One more more alpha-numberic, underscore, space or hyphen characters.

So it requires at least two characters to find a match.

If you take the second character set [a-zA-Z0-9_\s-] and exclude space and hyphen from it (as you require at the beginning of the string) then you get [a-zA-Z0-9_].

So, you want to match on:

^[a-zA-Z0-9_][a-zA-Z0-9_\s-]*$

• One character that can be alpha-numeric or an underscore (at the start of the string); then
• Zero or more subsequent alpha-numberic, underscore, space or hyphen characters.

Since \w is an equivalent regular expression character class to [a-zA-Z0-9_] then this can be simplified to:

^\w[\w\s-]*$

Answer 2

This regex should work:

^[\w-][\w\s-]*$

This will let first character be hyphen OR a alpha-num but rest 0 OR more characters be any combination of alpha-num OR space OR hyphen

Please note \w represents [A-Za-z0-9_]

If you only want first character to be alpha-num then use:

^\w[\w\s-]*$

Answer 3

So your string should not not start with "not space or hyphen" but rather the inverse: with 'a-z, 0-9, _'.

Try this instead:

^[a-zA-Z0-9_][a-zA-Z0-9_\s-]*$

One character in the first character class is required, and does not contain the space or hyphen. After that, anything goes -- zero or more times.