preg_match explanation?

[HARS]

hey all, this should be fairly easy to solve as i'm guessing this is a pretty basic question

i'm trying to check if a variable passed from a form is a valid address, containing letters, . or :
but php.net/preg_match doesn't help me much, somewhere between all the /\/// i get lost...

what i've scraped together is:

 //letters, . and :
  function isAddress($element) {
    return !preg_match ("/something here/", $element);
  } 

it would be nice if you could help me out here, ir send me off to some tutorial i haven't found yet... cheers!

[jinkas]

i'm not great with regexes, but if you want a tutorial there's a great one over at http://www.regular-expressions.info

[Darchangel]

// match letters commas periods and colons
function isAddress($element)
{ return !preg_match ("/[a-zA-Z,.: ]*/", $element); }

// match letters commas periods and colons AND numbers
function isAddress($element)
{ return !preg_match ("/[0-9a-zA-Z,.: ]*/", $element); } 

for a library of common regexs, also see: http://www.regexlib.com

[HARS]

ok, so you just add what you want to find between [ and ], nice. but what's with the * ? and i've seen ^ being used, but don't really know why.

[stereofrog]

> valid address, containing letters, . or :

your regexp is ~^[A-Za-z.:]+$~

where
~ is starting delimiter
^ means "beginning of search string"
[A-Za-z.:] is "uppercase letter or lowercase letter or dot or colon"
+ means "at least one"
$ is "end of search string"
~ is ending delimiter.

So,

function isAddress($str) {
   return preg_match("~^[A-Za-z.:]+$~", $str);
} 

note you don't need "!" (which means "not") before preg_match.

[HARS]

great! that is exactly the explanation i was looking for thanks!
i'm using ! 'cause i want it to return false if an element isn't found...