<?php
echo substr_count("Hello world. The world is nice","world");
?>

<?php
$str = "This is nice";
echo strlen($str)."<br>"; // Using strlen() to return the string length
echo substr_count($str,"is")."<br>"; // The number of times "is" occurs in the string
echo substr_count($str,"is",2)."<br>"; // The string is now reduced to "is is PHP"
echo substr_count($str,"is",3)."<br>"; // The string is now reduced to "s is PHP"
echo substr_count($str,"is",3,3)."<br>"; // The string is now reduced to "s i"
?>

<?php
$str = "abcabcab";
echo substr_count($str,"abcab"); // This function does not count overlapped substrings
?>

<?php
echo $str = "This is nice";
substr_count($str,"is",3,9);
?>