PHP - Check for whitespace at beginning of string

Question

I need to use preg_match to check that only a-z0-9. is used (including full stop(.)). I don't want to replace anything. My problem is that it doesn't notice white space at beginning of a string.

Also, if anyone knows how to check there is no two full stops in a row, I would be very grateful.

What I have so far:

("/[^a-z0-9.]+$/",$request)

Thanks !

Answer 1

You can do this without regex using ltrim'

if(ltrim($request) != $request) { // there was whitespace }

Answer 2

("/[^a-z0-9.]/",$request)

Edit - I misread your question. This will check to see if there are any non a-z0-9. characters.

Answer 3

^ inside [] negates characers (changes meaning to "any char except these")

^ outside of [] means "beggining of the string" (same as $ means "end of the string")

So you need something like that:

("/^[a-z0-9.]+$/",$request)

If you want to exclude sequences of dots but not single dots you need something bit more complicated:

preg_match('/^([a-z0-9]|(?<!\\.)\\.)+$/', $request);

Answer 4

/^(?!.*\.{2,}.*$)[a-z0-9.]+$/

Explanation

^          # start-of-string anchor
(?!        # begin negative look-ahead ("a position not followed by...")
  .*       # anything
  \.{2,}   # a dot, two times or more
  .*       # anything
  $        # the end of the string
)          # end negative lookahead
[a-z0-9.]+ # a-z or 0-9 or dot, multiple times
$          # end-of-string anchor

matches

• "abc"
• "abc123"
• "abc.123"

fails

• " abc"
• "abc..123"
• "abc!"