PHP ereg() is a deprecated function. It finds the specific pattern matches inside a string using regular expression. ereg() function is much slower than other string functions such as str_replace() which do not support regular expressions.

<?PHP
$str="2000-08-12T03:54:54Z";
if (ereg("\d",$str))
{
   echo "String contains number.";
}
?>

The matches can be stored into an array which is the 3rd parameter of the function.

<?PHP
$str="2000-08-12T03:54:54Z";
if (ereg("^((\d+)\-\d+\-\d+)T",$str,$mats))
{
   echo "$mats[0]";   //2000-08-12T
   echo "$mats[1]";   //2000-08-12
   echo "$mats[2]";   //2000
}
?>

ereg() is case sensitive. However, a similiar function eregi() is case insensitive.

<?PHP
$str="2000-08-12T03:54:54Z";
if (eregi("^((\d+)\-\d+\-\d+)t",$str,$mats))
{
   echo "$mats[0]";   //2000-08-12T
}
?>

Similiar functions include ereg_replace(), preg_match(), preg_replace(), str_replace().