Help with regular expressions and preg_match() in PHP

Hi everyone, I need help with regular expressions in PHP using the preg_match() function. I know how to allow only certain letters, numbers and/or characters. I need to be able to only allow only a set number of letters or numbers in an input field (for example, 3 or 4).

here is the code that I have so far:

// if the email field is empty, kill the function and display a message
if(!$email){
 die('Enter a name');
}
// allows only lower and uppercase letters and numbers
elseif(preg_match('/[^a-zA-Z0-9]/', $email)){
 die('Enter a valid email');
}
// outputs the email entered
else{
 echo "Email: $email";
}

PHP:

Thank You

 

// if the email field is empty, kill the function and display a message
if(!$email){
 die('Enter a name');
}
// allows only lower and uppercase letters and numbers
elseif(!preg_match('/^[a-z0-9]{3,4}$/i', $email_a)){
 die('Enter a valid email');
}
// outputs the email entered
else{
 echo "Email: $email";
}

PHP:

 

The code that you gave me worked and is self explanatory.

Thank You