The following example allows only number character in text field.
<script type=”text/javascript”>
function numberOnly(textField,e,isDecimal) {
// isDecimal = true for double
// isDecimal = false for integer
var key;
var keychar;
if (window.event) {
key = window.event.keyCode;
}
else if (e) {
key = e.which;
}
else {
return true;
}
// check double period,decimal,point
if ( ((textField.value).indexOf(‘.’) > -1) && key == 46){
alert(“Double period is not allow for this field.”);
return false;
}
var [...]

In web programming, sometimes we need to get the domain name out of the url. Here how to do it:
<?php
// get host name from URL
preg_match(‘@^(?:http://)?([^/]+)@i’, “http://www.php.net/index.html“, $matches);
$host = $matches[1];
// get last two segments of host name
preg_match(‘/[^.]+\.[^.]+$/’, $host, $matches);
echo “domain name is: {$matches[0]}\n”;
?>
What’s the hell that code means!

Here are list of functions that can be used to find a certain character in a string.

preg_match()
if (preg_match(“/php/i”, $string)) {
echo “A match was found. The string contains ‘php’ “;
} else {
echo “A match was not found.”;
}
ereg()
if(ereg(‘ ‘,$string)) echo ‘you have spaces’;
else echo ‘no spaces!’;
eregi()
if (eregi(‘z’, $string)) {
echo “‘$string’ contains a ‘z’ or [...]