How to complete a line?

Question

PHP

A string consisting of numbers comes conditionally into string examples

125687
159
1368

it is necessary that the line has 6 characters, but if a line comes with fewer digits, then you need to fill in 0, so I don’t understand how to do it yet.

Answer 1

php.net/manual/en/function.str-pad.php

Answer 2

Depending on how to set the task, with the addition of 0xD34F, he suggested that if you want to get a line like 000159 from line 159, then it is better to use sprintf...
php.net/manual/ru/function.sprintf.php
$num = 159;
sprintf('%06d', $num);