Replace string in text file using PHP

Does this work:

$msgid = $_GET['msgid'];

$oldMessage = '';

$deletedFormat = '';

//read the entire string
$str=file_get_contents('msghistory.txt');

//replace something in the file string - this is a VERY simple example
$str=str_replace($oldMessage, $deletedFormat,$str);

//write the entire string
file_put_contents('msghistory.txt', $str);

This works like a charm, fast and accurate:

function replace_string_in_file($filename, $string_to_replace, $replace_with){
    $content=file_get_contents($filename);
    $content_chunks=explode($string_to_replace, $content);
    $content=implode($replace_with, $content_chunks);
    file_put_contents($filename, $content);
}

Usage:

$filename="users/data/letter.txt";
$string_to_replace="US$";
$replace_with="Yuan";
replace_string_in_file($filename, $string_to_replace, $replace_with);

// never forget about EXPLODE when it comes about string parsing // it's a powerful and fast tool

Thanks to your comments. I've made a function that give an error message when it happens:

/**
 * Replaces a string in a file
 *
 * @param string $FilePath
 * @param string $OldText text to be replaced
 * @param string $NewText new text
 * @return array $Result status (success | error) & message (file exist, file permissions)
 */
function replace_in_file($FilePath, $OldText, $NewText)
{
    $Result = array('status' => 'error', 'message' => '');
    if(file_exists($FilePath)===TRUE)
    {
        if(is_writeable($FilePath))
        {
            try
            {
                $FileContent = file_get_contents($FilePath);
                $FileContent = str_replace($OldText, $NewText, $FileContent);
                if(file_put_contents($FilePath, $FileContent) > 0)
                {
                    $Result["status"] = 'success';
                }
                else
                {
                   $Result["message"] = 'Error while writing file';
                }
            }
            catch(Exception $e)
            {
                $Result["message"] = 'Error : '.$e;
            }
        }
        else
        {
            $Result["message"] = 'File '.$FilePath.' is not writable !';
        }
    }
    else
    {
        $Result["message"] = 'File '.$FilePath.' does not exist !';
    }
    return $Result;
}