The PHP ftp_nb_get() function downloads a file from the FTP server and saves it into a local file (non-blocking).

<?php
// connect and login to FTP server
$ftp_server = 'ftp.example.com';

$ftp_conn = ftp_connect($ftp_server) or die('Could not connect to ' . $ftp_server);
$login = ftp_login($ftp_conn, $ftp_username, $ftp_userpass);

// open files
$local_file = 'local.txt';
$server_file = 'server.txt';

// initiate download
$d = ftp_nb_get($ftp_conn, $local_file, $server_file, FTP_ASCII);

while ($d == FTP_MOREDATA) {
    // do something

    // continue downloading
    $d = ftp_nb_continue($ftp_conn);
}

if ($d != FTP_FINISHED) {
    echo 'Error downloading file';
    exit(1);
}

// close connection
ftp_close($ftp_conn);
?>

// downloads a file from the FTP server (non-blocking) and saves it to a local file

ftp_nb_get(ftp_conn, local_file, server_file, mode, startpos)