The File Transfer Protocol (FTP) is widely used to transfer files across networks. Utilising it in a PHP script allows you to increase the level of sophistication of your PHP scripts as well as learn more about how FTP works. Before proceeding, get the details of an FTP account to which you have read and write access. For example, most Internet service providers give users an account on their Web servers to host a small amount of data, to which access is generally provided via FTP.

Alternatively, if you have your own UNIX or Linux system, you should already have an FTP server.

Installation

The FTP extension needs no additional libraries to make it work, but you must recompile PHP. To include FTP support, run the following in the PHP source directory:

./configure --enable-ftp [other options]

The --enable-ftp argument configures FTP support to be added. If you want to include support for other extensions, such as PostgreSQL, be sure to specify their respective arguments to the configure script. Then it is just a matter of compiling and installing the FTP-enabled version of PHP. For more information on this process, see the INSTALL file in the PHP source directory.

A basic FTP session

A basic FTP session involves connecting to an FTP server, logging in with a username and password, interacting with the server and closing the connection. The following script can be used to do this:

01     <?
02     $HOST="somehost.com.au";
03     $UN="username";
04     $PW="password";
05     $DIR="/remote/directory/";
06     $FILE="test.txt";
07
08     $conn = ftp_connect($HOST);
09     if(!$conn) {
10        exit("Could not connect to server: $HOST\n");
11    }
12
13    if(!ftp_login($conn,$UN,$PW)) {

14        ftp_quit($conn);
15        exit("Could not log in\n");
16    }
17
18    ftp_chdir($conn,$DIR);
19
20    $files = ftp_nlist($conn,".");
21
22    for($i=0;$i<count($files);$i++) {
23        if(!ftp_get($conn,$files[$i],$files[$i],FTP_ASCII)) {
24            echo "Could not download {$files[$i]}\n";
25        }
26    }
27
28    if(!ftp_put($conn,$DIR.$FILE,$FILE,FTP_ASCII)) {
29        echo "Could not upload $FILE\n";
30    }
31
32    ftp_quit($conn);
33    ?>

Lines 02 through 06 define some parameters that will be specific to your setup. Set $HOST to an FTP server to which you have access; set $UN and $PW to the username and password, respectively, for the server; set $DIR to a directory on the remote server to which you have read and write access; and set $FILE to a local file you want to upload to the remote server.

On line 08, the script attempts to connect to $HOST - if it cannot, it fails out. On line 13, the script sends the username and password information required to authenticate access with the server. If the username and/or password are incorrect - or if there is an error - we exit from the script, informing the user. The script also tidies up after itself, closing the FTP session using ftp_quit().

If all goes well, on line 18 the script changes to the remote directory $DIR. On line 20, we retrieve a list of files in $DIR using the ftp_nlist() function. This function returns an array of files names. On lines 22 through 26, the script loops through the files, retrieving each (line 23) using ftp_get(). The second argument to ftp_get() specifies the local filename to which the remote file will be downloaded. The third argument specifies the remote file in which we are interested.

Finally, the fourth argument is the mode in which to download the file. There are two modes: FTP_ASCII for ASCII or text files; and FTP_BINARY for files in binary format, such as images or executables. Generally speaking, the mode that is chosen only matters if the client, server or both are not UNIX systems. The script uses FTP_ASCII. If any error is encountered when trying to download a file, the script notifies the user. On line 28, the script attempts to upload $FILE to the remote server using ftp_put(). The second argument specifies the remote file name, while the third specifies the local filename. As with ftp_get(), the fourth argument is the mode in which to transfer the file. If an error is encountered, the script tells the user.

The FTP session is closed on line 32 using ftp_quit().