8 basics of regular expression that can make you expert

Well, regular expressions have been something that I was scared of when I started coding as a serious stuff. The string literals puzzled me like anything. preg_match, preg_grep, preg_split, preg_replace etc have been something I always wanted to avoid. But thanks to phpbuilder and php that I can now handle them with some ease. And this is for you guys who find regular expressions tacky.


VERY BASICS:
1. "^tech" : Searches a string that starts with tech.
2. "logy$" : Searches for strings that ends up in logy.
3. "a*b" : Looks for a string that has either zero or more a’s but exactly one b following a. (eg. b, ab, aab, aaab, aaaaaaaaaaaaaaaaab etc.).
4. "a+b" : Same as a*b but only difference is that atleast one a should be there in the string unlike a*b which can overlook a. (eg. ab, aab,aaaaaaaaab etc).

Date and Time validation using Regular Expression

This function is used for date validation on a string
Return of this function is boolean.
function is_date($str){
   $return = (bool) preg_match("(\b([1-9]([0-9]{3}))\-(1[0-2]|0[1-9])\-(3[01]|[12][0-9]|0[1-9])\b)",$str);
   if(strlen($str)==10){
      return $this->is_date_time($str);
   }
   if($return){
     $return = (bool) (strlen($str)==10);
   }
   return $return;
}

This function is used for time validation on a string
Return of this function is boolean.
function is_time($str){
   $return = (bool) preg_match("(\b(2[0-3]|[01][0-9])\:([0-5][0-9])\:([0-5][0-9])\b)",$str);
   if($return){
      $return = (bool) (strlen($str)==8);
   }
   return $return;
}


And This function is used for date_time validation on a string
Return of this function is boolean.
function is_date_time($str){
   $return = (bool) preg_match("(\b([1-9]([0-9]{3}))\-(1[0-2]|0[1-9])\-(3[01]|[12][0-9]|0[1-9]) (2[0-3]|[01][0-9])\:([0-5][0-9])\:([0-5][0-9])\b)",$str);
   if($return){
      $return = (bool) (strlen($str)==19);
   }
   return $return;
}

URI Validation Using Regular Expression

who know about regular expression?
i need to validate a uri.
so create a validation script using preg_match() on PHP.
but, i get something wrong with my script. can you help me?

this is my uri validation function:
function valid_uri($str){
$patern = "/^((ht|f)tp(s?)\:\/\/|)([a-z0-9]([-.]*[a-z0-9])*(:(0-9)*)*([\/][a-zA-Z0-9\-\.\?\,\/\\\+&%\$#_=]*))?+$/i";
return preg_match($patern,$str);
}

and I have been tested:
$tes=array( "http://www.amikom.ac.id", "amikom.ac.id", "amikom.ac.id.", "ihi amikom.ac.id aha", "https://email.amikom.ac.id","www..com", "http://e-learning.com/", "e-learning.com/index.php", "e-learning.com/index.php?x=1234&a=897", "bukan uri","anang.",".anang.",".com", "http://.com","saya.#@%\$#ini.com");
foreach($tes as $item){
echo "\n".(($this->validasi->valid_uri($item))?"yes":"no")." ".$item;
}

and this is the result:
yes http://www.amikom.ac.id
no amikom.ac.id
no amikom.ac.id.
no ihi amikom.ac.id aha
yes https://email.amikom.ac.id
no www..com
yes http://e-learning.com/
yes e-learning.com/index.php
yes e-learning.com/index.php?x=1234&a=897
no bukan uri
no anang.
no .anang.
no .com
yes http://.com
no saya.#@%$#ini.com

".com" is not valid url, but why "http://.com" is valid?
i just stuck here.
anyone can help me?