if you for some reason need to get lines from a string instead of a file pointer, try
<?php
function string_gets(string $source, int $offset = 0, string $delimiter = "\n"): ?string
{
 $len = strlen($source);
 if ($len < $offset) {
 // out of bounds.. maybe i should throw an exception
 return null;
 }
 if ($len === $offset) {
 // end of string..
 return null;
 }
 $delimiter_pos = strpos($source, $delimiter, $offset);
 if ($delimiter_pos === false) {
 // last line.
 return substr($source, $offset);
 }
 return substr($source, $offset, ($delimiter_pos - $offset) + strlen($delimiter));
}
?>

(i had a ~16GB string in-memory i needed to process line-by-line, but i would get memory-allocation-crash (on a 32GB ram system) if i tried explode("\n",$str); , so came up with this.. interestingly, fgets() seems to be faster than doing it in-ram-in-php, though. php 7.3.7)