Need to match any string that contains [a-z0-9\x20] but with no spaces at the start or end and no double spaces

Question

So far I have

^[a-z0-9]+[a-z0-9\x20]+[a-z0-9]+$

Which matches all criteria except not matching double spaces.

Answer 1

Try this:

^[a-z0-9](?: ?[a-z0-9])*$

As seen on rubular

a_bc   # match (underscore '_' represents space)
abc    # match
a_     # no match
_a     # no match
a__b   # no match

(You can replace the whitespace after the ?: with \x20 if you have to)

Answer 2

Something along these lines should work:

^[a-z0-9]+((\x20)?[a-z0-9]+)*$

This will mean you can have letter or number at the start, one or more times, followed by a block containing a space 0 or 1 times, followed by 1 or more letters or numbers, which can be included 0 or more times.

Edit: I think this should work. Can only have 0 or 1 spaces in between blocks of letters/numbers.

Answer 3

How about:

^[a-z0-9]+(\x20[a-z0-9]+)*$

One or more letter or numbers, followed by a space & one or more letters/numbers, repeated 0 or more times.