Few commonly used regular expressions

// find email address
$str = "asdf fasf afdd d pawan269@gmail.com adfsdf asdf";
$find = "/[a-zA-Z0-9._]+@[a-zA-Z0-9]+.[a-zA-Z]{2,5}/";
preg_match_all($find, $str, $matches);
print_r($matches);

// find all domain names
$str = "asfasd fasdf asdfas dfa http://google.com sdf www.GOOGLE.com asd fasd http://www.google.com fasd fdfdf ";
$find = "@[http://|www.]+[a-zA-Z0-9]+.[a-zA-Z]{2,5}@";
preg_match_all($find, $str, $matches);
print_r($matches);

// will take out last 4 chars
$str = "SG-7-ABCD";
$find = "/[a-zA-Z]{4}$/";
preg_match_all($find, $str, $matches);
print_r($matches);

// will take out first 3 chars
$str = "xyz-23";
$find = "/^[a-zA-Z]{3}/";
preg_match_all($find, $str, $matches);
print_r($matches);

// find all hex color code in a string
$str = "asdfas fa #FF22FF adsf #DFDFDF dsfasf #123456 afsd f";
$find = "/[#0-9a-fA-F]{7}/";
preg_match_all($find, $str, $matches);
print_r($matches);

// find date (mysql format) in string
$str = "asdf fasf afdd d 2010-04-12 17:20:25 adfsdf asdf";
$find = "/[0-9]{4}+-[0-9]{2}+-[0-9]{2} [0-9]{2}+:[0-9]{2}+:[0-9]{2}/";
preg_match_all($find, $str, $matches);
print_r($matches);