Recipe 18.2 Being an FTP Client

18.2.1 Problem

You want to connect to an FTP server and transfer files. For example, you might want to automate the one-time transfer of many files or automatically mirror an entire section of an FTP server.

18.2.2 Solution

Use the Net::FTP module:

use Net::FTP;

$ftp = Net::FTP->new("ftp.host.com")    or die "Can't connect: $@\n";
$ftp->login($username, $password)       or die "Couldn't login\n";
$ftp->cwd($directory)                   or die "Couldn't change directory\n";
$ftp->get($filename)                    or die "Couldn't get $filename\n";
$ftp->put($filename)                    or die "Couldn't put $filename\n";

18.2.3 Discussion

Using the Net::FTP module is a three-part process: connect to a server, identify and authenticate yourself, and transfer files. All interaction with the FTP server happens through method calls on a Net::FTP object. If an error occurs, methods return undef in scalar context or the empty list in list context.

The connection is established with the new constructor. If an error occurs, $@ is set to an error message and new returns undef. The first argument is the hostname of the FTP server, optionally followed by named options:

$ftp = Net::FTP->new("ftp.host.com",
                     Timeout => 30,
                     Debug   => 1)
    or die "Can't connect: $@\n";

The Timeout option gives the number of seconds all operations wait before giving up. Debug sets the debugging level (non-zero sends copies of all commands to STDERR). Firewall takes a string as an argument, specifying the machine acting as an FTP proxy. Port lets you select an alternate port number (the default is 21, the standard port for FTP). Finally, if the Passive option is set to true, all transfers are done passively (some firewalls and proxies require this). The Firewall and Passive options override the environment variables FTP_FIREWALL and FTP_PASSIVE.

Having connected, the next step is to authenticate. Normally, you'll want to call login with up to three arguments: username, password, and account.

$ftp->login( )
    or die "Couldn't authenticate.\n";

$ftp->login($username)
    or die "Still couldn't authenticate.\n";

$ftp->login($username, $password)
    or die "Couldn't authenticate, even with explicit username
            and password.\n";

$ftp->login($username, $password, $account)
    or die "No dice.  It hates me.\n";

If you call login with no arguments, Net::FTP uses the Net::Netrc module to find settings for the host you've connected to. If none are found, anonymous login is attempted (username anonymous, password -anonymous@). If no password is given and the username anonymous is used, the user's mail address is supplied as the password. The optional account argument is not used on most systems. If the authentication fails, login returns undef.

Once authenticated, the usual FTP commands are available as methods called on your Net::FTP object. The get and put methods fetch and send files, respectively. To send a file, use:

$ftp->put($localfile, $remotefile)
    or die "Can't send $localfile: $!\n";

If you omit the second argument, the remote file will have the same name as the local file. You can also send from a filehandle (in which case the remote filename must be given as the second argument):

$ftp->put(*STDIN, $remotefile)
    or die "Can't send from STDIN: $!\n";

If the transfer is interrupted, the remote file is not automatically deleted. The put method returns the remote filename if it succeeded, or undef on error.

To fetch a file, use the get method, which returns the local filename, or undef on error:

$ftp->get($remotefile, $localfile)
    or die "Can't fetch $remotefile : $!\n";

You can also get into a filehandle, in which case the filehandle is returned (or undef on error):

$ftp->get($remotefile, *STDOUT)
    or die "Can't fetch $remotefile: $!\n";

Pass get an optional third argument, representing an offset into the remote file, to begin the transfer at that offset. Received bytes are appended to the local file.

The type method changes the file translation mode. Pass it a string ("A", "I", "E", or "L") and it will return the previous translation mode. The ascii, binary, ebcdic, and byte methods call type with the appropriate string. If an error occurs (the FTP server does not do EBCDIC, for example), type and its helper methods return undef.

Use cwd($remotedir) and pwd to set and fetch the current remote directory. Both return true if successful, false otherwise. If you cwd(".."), the cdup method is called to change the directory to the parent of the current directory. Call cwd without an argument to change to the root directory.

$ftp->cwd("/pub/perl/CPAN/images/g-rated");
print "I'm in the directory ", $ftp->pwd( ), "\n";

mkdir($remotedir) and rmdir($remotedir) make and delete directories on the remote machine. You have the built-in mkdir and rmdir functions to make and delete empty directories on the local machine. To create all directories up to the given directory, pass a true second argument to mkdir. For instance, to create /pub, /pub/gnat, and /pub/gnat/perl directories, say:

$ftp->mkdir("/pub/gnat/perl", 1)
    or die "Can't create /pub/gnat/perl recursively: $!\n";

If mkdir succeeds, the full path to the newly created directory is returned; otherwise, it returns undef.

The ls and dir methods retrieve a list of files in a remote directory. Traditionally, dir gives you a more verbose listing than ls, but neither has a standard format. Most Unix FTP servers return the output of ls and ls -l respectively, but you can't guarantee that behavior from every FTP server. In list context, these methods return the list of lines returned by the server. In scalar context, they return a reference to an array containing those lines.

@lines = $ftp->ls("/pub/gnat/perl")
    or die "Can't get a list of files in /pub/gnat/perl: $!";
$ref_to_lines = $ftp->dir("/pub/perl/CPAN/src/latest.tar.gz")
    or die "Can't check status of latest.tar.gz: $!\n";

When you're done and want to finish gracefully, use the quit method:

$ftp->quit( )    or warn "Couldn't quit.  Oh well.\n";

Other methods rename, change ownership and permissions of remote files, check the size of the remote file, and so on. Read the Net::FTP documentation for details.

To mirror files between machines, use the excellent mirror program written in Perl by Lee McLoughlin. Look for it on the Web at http://sunsite.doc.ic.ac.uk/packages/mirror/.