validate user entry to have no spaces.

I'm trying to write a script to validate a legal php variable name, but I can't seem to make it work so it doesn't validate spaces.  Any help would be much appreciated!

Here's my code:

    
<fieldset><legend><h1>PHP Variable Validator</h1></legend>
    
    <p>A valid PHP variable begins with the dollar sign ("$") followed by either a letter or underscore ("_") followed by any series of numbers, letters or underscores.</p>
    <p>Ex: $variable</p>
<form action="name_validator.php" method="post">
      <input name="variable" type="text" />
      <input name="submit" type="submit" value="Validate it!" />
    </form>


<?php
$variable = $_POST['variable'];

if ($variable == "quit") {
echo "Thanks for trying the validator!";
}
elseif (preg_match("/^[$][a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*/",$variable)) {
   echo "<b>" . $variable . "</b>" . " is a valid PHP variable name";
} 
elseif (!isset($variable)) {
   	echo ""; 
} 
else {
 echo "<b>" . $variable . "</b>" . " is not a valid PHP variable name";
}

?>

</fieldset>

You need a $ anchor to ensure the expression matches the entire string, rather than just an initial length of it.