Create random string in PHP Smarty template - php

Question

I have the following input field:
{assign var="name" value="test12345.example.com"}
<input name="domain" value="{$domain}" size="50"
data-hostname-check="{$options}"
placeholder="<?php echo substr(md5(mt_rand()), 0, 7); ?>"
onchange="if (
typeof simulateCart == 'function' && this.checkValidity())
simulateCart.call(this);"/>
What i need is to generate a random string for if the input field when its not filled. But I have no clue how to do this. This input field is in an if loop using smarty template.
The onchange is required at the moment so if I remove this you can leave the input field blank but there should be a label before we can insert it into the database
At the moment I have a var (static) whichh i can use for the placeholder text. The echo which i tried does not work. Maybe someone can help me fixing this. If i put this in the placeholder the whole text in the "" will be displayed.
Another issue is that the form has an input validation and you have to press on a button. I know there is an jQuery on.click how can i use this in my situation.

Answer 1

You can write smarty plugin wich will output random string.
See chapter "function plugin with output" here https://www.smarty.net/docs/en/plugins.functions.tpl
You need only create file with you functuion
function smarty_function_randomstring($params, Smarty_Internal_Template $template) {
return substr(md5(mt_rand()), 0, 7);
}
Ant put it in plugin directory https://www.smarty.net/docs/en/variable.plugins.dir.tpl
Then you can use it in smarty like this
<input placeholder="{randomstring}"