Question

I’m new to Regular Expressions…
I’ve been asked a regular expression that accepts Alphanumerics, a few characters more, and only ONE whitespace between words.

For example :
This should match :

"Hello world"

This shouldn’t :

"Hello  world"

Any ideas?

This was my expression:

[\w':''.'')''(''\[''\]''{''}''-''_']+$

I already tried the \s? (the space character once or never – right? ) but I didn’t get it to work.

Answer 1

Using Oniguruma regex syntax, you could do something like:

^[\w\.:\(\)\[\]{}\-_](?: ?[\w\.:\(\)\[\]{}\-_])*$

Assuming that the ‘other characters’ are . : () [] {} – _

This regex will match a string that must begin and end with a word character or one of the other allowed characters and cannot have more than one space in a row.

If you’re using the x flag (ignore whitespace in regular expression) you’ll need to do this instead:

^[\w\.:\(\)\[\]{}\-_](?:\ ?[\w\.:\(\)\[\]{}\-_])*$

The only difference is the \ in front of the space.