Insert string at specified position in PHP

<?php
$sentence = 'I am happy today.';
$string = 'very ';
$position = '5';

echo substr_replace( $sentence, $string, $position, 0 );
?>

<?php
function insertString($sentence, $string, $position) {
    // Ensure position is within bounds of the sentence
    if ($position < 0 || $position > strlen($sentence)) {
        return "Invalid position";
    }
    
    // Insert the string at the specified position
    $newSentence = substr($sentence, 0, $position) 
      	. $string . substr($sentence, $position);
    
    return $newSentence;
}


$sentence = 'I am happy today.';
$string = 'very';
$position = 4;
$newSentence = insertString($sentence, $string, $position);
echo $newSentence; // Output: I amvery happy today.

?>

<?php
// Function to insert a string at a specified position
function insertStringAtPosition($sentence, $stringToInsert, $position) {
    // Split the sentence into two parts at the specified position
    $part1 = substr($sentence, 0, $position);
    $part2 = substr($sentence, $position);

    // Concatenate the parts with the string to be inserted
    $newSentence = $part1 . $stringToInsert . $part2;

    return $newSentence;
}


$sentence1 = 'I am happy today.';
$string1 = 'very ';
$position1 = 5;

$sentence2 = 'I am happy today.';
$string2 = ' very';
$position2 = 4;

echo insertStringAtPosition($sentence1, $string1, $position1) . "\n"; 
echo insertStringAtPosition($sentence2, $string2, $position2) . "\n"; 
?>