Truncate a string up to a certain length, preserving whole words

str_truncate.php

<?php

function str_truncate($str, $limit, $ellipsis = '...') {
    if (strlen($str) <= $limit) {
        return $str;
    }

    $limit -= strlen($ellipsis);
    $pos = strrpos($str, ' ', $limit - strlen($str));
    if ($pos === false) {
        $pos = $limit;
    }
    
    return substr($str, 0, $pos).$ellipsis;
}

function str_truncate2($str, $limit, $ellipsis = '...') {
    $limit -= strlen($ellipsis);
    return rtrim(preg_replace("/^(.{0,$limit})\\b.*/", '$1', $str)).$ellipsis;
}

test.php

<?php

include("str_truncate.php");
$string = "the quick brown fox jumps over the lazy dog";

for($limit = 10; $limit <= strlen($string); $limit += 10) {
    print_r(str_truncate($string, $limit));
}

for($limit = 10; $limit <= strlen($string); $limit += 10) {
    print_r(str_truncate2($string, $limit));
}