Swap the letters of the beginning of an email with another character

Question

I’m trying to replace letters with asterisks of an email using the preg_replace() php, but php takes all the letters in the email, but I just want to put the asterisks in the first letters. example:

input: [email protected] exit: *********[email protected]

But my code is taking all the letters and replacing them with asterisks for example: input: [email protected]
exit: *********2020@*****.***

my code:

<?php 
    $email="[email protected]";

    $emailRegex=preg_replace('/([a-z])/','*', $email);
    
    echo $email;
    echo "<br>";
    echo $emailRegex;

Answer 1

No need to regex, just go through the string and swap the letters for asterisks. When you find something that is not letter, stop:

for ($i = 0; $i < strlen($email); $i++) {
    if (ctype_lower($email[$i]))
        $email[$i] = '*';
    else break;
}
echo $email;

I used ctype_lower which checks if it’s a lowercase letter. If it is, I change it to an asterisk, and if it’s not I interrupt the loop.

---

But if you really want to use regex:

function troca($m) {
  return str_repeat('*', strlen($m[1])). $m[2];
}
$email="[email protected]";
$emailRegex=preg_replace_callback('/^([a-z]+)(\d*@.+)$/', 'troca', $email);
    
echo $emailRegex;

I create 2 capture groups (indicated by the parentheses): one with the beginning letters and the other containing the numbers on. I use \d* to indicate zero or more digits (in case you don’t have any), then the @, and .+ (one or more characters) to go to the end of the string. I also use the markers ^ and $, which indicate respectively the start and end of the string.

Then I create a substitution function, which takes the first group, checks the size and generates another string of the same size, but containing only asterisks - is what str_repeat makes. Then I concatenate with the second group, which contains the rest of the string.

The difference is that to use the function I must use preg_replace_callback instead of preg_replace.

Particularly I prefer the first option. Regex even works but it seems to me unnecessarily complicated for your case.

Remembering that no solution validates if the string is in fact an email.