error message shows up when page loads

[pikebro2002]

i want to display an error message if the form is submitted without an email address given, but i am having problems since the form starts out with no value in the email field so the error message has already appeared when the page loads. i tried a few different ways. any suggestions would be greatly appreciated. thanks!

<?php

$email = $_POST["email"];

if(eregi('', $email))
{
$noEmail = 'error';
echo "<FONT COLOR=\"red\"> Please enter a valid email address! </FONT><br>";

}

?>

and

<?php

$email = $_POST["email"];

if(empty($email))
{
$noEmail = 'error';
echo "<FONT COLOR=\"red\"> Please enter a valid email address! </FONT><br>";

}

?>

and

<?php

$email = $_POST["email"];

if($email == '')
{
echo "<FONT COLOR=\"red\"> Please enter a valid email address! </FONT><br>";
$noEmail = 'error';

}

?>

[devinemke]

<?php
if (!isset($_POST['submit']))
{
	echo '
	<form action="" method="POST">
	email: <input type="text" name="email">
	<input type="submit" name="submit" value="submit">
	</form>
	';
}
else
{
	$form_check = true;
	$email = trim($_POST['email']);

if (!eregi("^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*$", $email))	{$form_check = false;}

if ($form_check) {echo 'valid email: ' . $email;}
else {echo '<font color="red">invalid email: ' . $email . '</font>';}
}
?>

[pikebro2002]

thanks i got it working, i did it a little different however.