php substring regex

I've been reading php code all day and what I can't seem to find an answer to what I believe is a simple question.

I've got an array full of strings and I want to see if the first character in a string is a number, then do something with it, e.g:

if substr($stringArray[$i],0,1) == regexsomething[0-9]) { do stuff }

Have I got this all wrong?

Surely I could set the regex to be [^0-9] to match at the start but the PHP preg_match is confusing me greatly.

Any advice would be super.

Than开发者_高级运维ks

Outside brackets, ^ means "start", but right after a [, it means "invert this whole class". /[^0-9]/ would match anything that contains a non-digit. A regular expression to match a single digit would be:

/^[0-9]$/

PHP already has a function for this, though: is_numeric()

if ( is_numeric( substr( $stringArray[$i],0,1 ) ) ) { do stuff }

If you want to go the regex route, you won't need to get the first character. A regex that matches anything that starts with a digit would be:

if ( preg_match( '/^[0-9]/', $stringArray[$i] ) ) { do stuff }

If you wnat to make sure that a string is a number you can use is_numeric like so:

if(is_numeric($string))
{
    //Do Something
}

If you want to make sure its a single digit like 7 you can use the < less-than operator

if(is_numeric($string) && $string < 10)
{
    //Do Something
}