Stop Receiving Blank Emails!

Hello,

How can I make it so my script will not allow people to hit submit until the have filled in the required field/s because if you hit submit without entering anything I get a blank email which is a little annoying.

HTML

<form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
<p>Name:<br>
<input name="name" type="text" />
 </p>
<p>Email:<br>
<input name="email" type="text" />
 </p>
<p>Subject:<br>
<input name="subject" type="text" />
 </p>
<p>Message:<br>
<textarea name="message" rows="6"></textarea>
 <br />
<input type="submit" value="Send" /><input type="hidden" name="do" value="send" /><input type="reset" value="Reset" />
 </p></form>

Code (markup):

PHP

<?php
if($_POST['do']=="send") {
$recipient="Email"; // Set your email here //
$subject=$_POST['subject'];
$name=$_POST['name'];
$email=$_POST['email'];
$message = "Name: {$name}\n\nMessage:\n{$_POST['message']}";
$formsend=mail("$recipient", "$subject", "$message", "From: $name ($email)\r\nReply-to:$email");
echo("<p>Your message was successfully sent!</p>");
}
?>

Code (markup):

Thanks in advance!

 

A very simple way

<?php
$errors = array();
if($_POST['do']=="send") {
  $recipient="Email"; // Set your email here //
  if (!$subject=$_POST['subject']) $errors[] = 'Subject required';
  if (!$name=$_POST['name']) $errors[] = 'Name required';
  if (!$email=$_POST['email']) $errors[] = 'Email required';
  if (!$message=$_POST['message']) $errors[] = 'Message required';
  if (!$errors) {
    $message = "Name: {$name}\n\nMessage:\n{$message}";
    $formsend=mail("$recipient", "$subject", "$message", "From: $name ($email)\r\nReply-to:$email");
    echo("<p>Your message was successfully sent!</p>");
  }
}
?>

PHP:

And in your HTML:

<form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
<?php if ($errors) echo '<p>The following errors occurred: <br />' . join('<br />', $errors) . '</p>'; ?>
<p>Name:<br>
<input name="name" type="text" />
 </p>
<p>Email:<br>
<input name="email" type="text" />
 </p>
<p>Subject:<br>
<input name="subject" type="text" />
 </p>
<p>Message:<br>
<textarea name="message" rows="6"></textarea>
 <br />
<input type="submit" value="Send" /><input type="hidden" name="do" value="send" /><input type="reset" value="Reset" />
 </p></form>

Code (markup):

 

Awesome, thank you!

 

It would also a good practice to have both sides validation. krt proposal is correct, but i would add Javascript validations to avoid useless execution of the server script.