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Unix on Panther: Accessing the Internet
Pages: 1, 2, 3

Transferring Files

You may need to copy files between computers. For instance, you can put a backup copy of an important file you're editing onto an account at a computer in another building or another city. Or, Dr. Nelson could put a copy of a data file from her local computer onto a central computer, where her colleagues can access it. Or you might want to download 20 files from an FTP server, but not want to go through the tedious process of clicking on them one by one in a web browser window. If you need to do this sort of thing often, you may be able to set up a networked filesystem connection; then you'll be able to use the Finder or local programs such as cp and mv. But Unix systems also have command-line tools for transferring files between computers. These often work more quickly than graphical tools. We explore them later in this section.

scp and rcp

Mac OS X includes both scp (secure copy) and rcp (remote copy) programs for copying files between two computers. In general, you must have accounts on both computers to use these. The syntax of scp and rcp are similar to cp, but also let you add the remote hostname to the start of a file or directory pathname. The syntax of each argument is:

hostname:pathname

hostname: is needed only for remote files. You can copy from a remote computer to the local computer, from the local computer to a remote computer, or between two remote computers.

The scp program is much more secure than rcp, so we suggest using scp to transfer private files over insecure networks such as the Internet. For privacy, scp encrypts the file and your passphrase.

For example, let's copy the files report.may and report.june from your home directory on the computer named giraffe.intuitive.com and put the copies into your working directory (.) on the machine you're presently logged in to. If you haven't set up the SSH agent that lets you use scp without typing your passphrase, scp will ask you:

$ scp giraffe.intuitive.com:report.may giraffe.intuitive.com:report.june .
Enter passphrase for RSA key 'taylor@mac':

To use wildcards in the remote filenames, put quotation marks ("name") around each remote name.[2] You can use absolute or relative pathnames; if you use relative pathnames, they start from your home directory on the remote system. For example, to copy all files from your food/lunch subdirectory on your giraffe account into your working directory (.) on the local account, enter:

$ scp "giraffe.intuitive.com:food/lunch/*" .

Unlike cp, the Mac OS X versions of scp and rcp don't have an -i safety option. If the files you're copying already exist on the destination system (in the previous example, that's your local machine), those files are overwritten.

If your system has rcp, your system administrator may not want you to use it for system security reasons. Another program, ftp, is more flexible and secure than rcp (but much less secure than scp).

FTP

FTP, or file transfer protocol, is a standard way to transfer files between two computers. Many users of earlier Mac OS versions are familiar with Fetch (http://fetchsoftworks.com/), a shareware graphical FTP client that runs on Mac OS X as well as earlier versions.

The Unix ftp program does FTP transfers from the command line. There are also a number of easy-to-use graphical FTP tools available from the Apple web site (go to "Get Mac OS X Software . . . " from the Apple menu and click on Internet Utilities). But we cover the standard ftp program here. The computers on either end of the FTP connection must be connected by a network (such as the Internet).

To start FTP, identify yourself to the remote computer by giving the username and password for your account on that remote system. Unfortunately, sending your username and password over a public network means that snoopers might see them—and use them to log into your account on that system.

A special kind of FTP, anonymous FTP, happens if you log into the remote server with the username anonymous. The password is your email address, such as alex@foo.co.uk. (The password isn't usually required; it's a courtesy to the remote server.) Anonymous FTP lets anyone log into a remote system and download publicly accessible files to their local systems. Here's how that might look:

$ ftp ftp.apple.com
Trying 17.254.16.11...
Connected to ftp.apple.com.
220 ProFTPD 1.2.8 Server (Apple Anonymous FTP Server) [ftp02.apple.com]
Name (ftp.apple.com:taylor): ftp
331 Anonymous login ok, send your complete email address as your password.
Password:
230 Anonymous access granted, restrictions apply.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> dir
500 EPSV not understood
227 Entering Passive Mode (17,254,16,11,223,250).
150 Opening ASCII mode data connection for file list
drwxrwxrwx   3 ftpprod  ftpprod       102 May  7 19:11 Apple_Support_Area
drwxrwxr-x  20 ftpprod  ftpprod       680 Aug 28 22:07 developer
drwxrwxr-x  30 ftpprod  ftpprod      1020 Sep 15 13:44 emagic
drwxrwxr-x  10 ftpprod  ftpprod       340 Sep  3 16:23 filemaker
drwxrwxrwx  10 ftpprod  ftpprod       340 Apr  7 16:50 research
226 Transfer complete.
ftp> quit
221 Goodbye.
$

Command-line ftp

To start the standard Unix ftp program, provide the remote computer's hostname:

ftp hostname

ftp prompts for your username and password on the remote computer. This is something like a remote login (see Section 8.1, earlier in this chapter), but ftp doesn't start your usual shell. Instead, ftp prints its own prompt and uses a special set of commands for transferring files. Table 8-1 lists the most important ftp commands.

Table 8-1. Some ftp commands

Command

Description

put filename

Copies the file filename from your local computer to the remote computer. If you give a second argument, the remote copy will have that name.

mput filenames

Copies the named files (you can use wildcards) from the local computer to the remote computer.

get filename

Copies the file filename from the remote computer to your local computer. If you give a second argument, the local copy will have that name.

mget filenames

Copies the named files (you can use wildcards) from the remote computer to the local computer.

prompt

A "toggle" command that turns prompting on or off during transfers with the mget and mput commands. By default, mget and mput will prompt you "mget filename?" or "mput filename?" before transferring each file; you answer y or n each time. Typing prompt once, from an ftp> prompt, stops the prompting; all files will be transferred without question until the end of the ftp session. Or, if prompting is off, typing prompt at an ftp> prompt resumes prompting.

hash

Displays progress marks on file uploads and downloads so you can gauge progress. Particularly helpful with large transfers.

cd pathname

Changes the working directory on the remote machine to pathname (ftp typically starts at your home directory on the remote machine).

lcd pathname

Changes ftp's working directory on the local machine to pathname. (ftp's first local working directory is the same working directory from which you started the program.) Note that the ftp lcd command changes only ftp's working directory. After you quit ftp, your shell's working directory will not have changed.

dir

Lists the remote directory (like ls -l).

binary

Tells ftp to copy the file(s) that follow it without translation. This preserves pictures, sound, or other data.

ascii

Transfers plain-text files, translating data if needed. For instance, during transfers between a Microsoft Windows system (which adds Control-M to the end of each line of text) and a Unix system (which doesn't), an ascii-mode transfer removes or adds those characters as needed.

passive

Toggles the setting of passive mode. This may help ftp to run correctly if you are behind a firewall. If you put the command setenv FTP_PASSIVE 1 in your .tcshrc, all your ftp sessions will use passive mode.

quit

Ends the ftp session and takes you back to a shell prompt.

Here's an example. Carol moves into the local directory she wants to use as a starting point (a good idea whether you're uploading or downloading), then uses ftp to copy the file todo from her work subdirectory on her account on the remote computer rhino:

$ cd uploads
$ ls
afile   ch2    somefile
$ ftp rhino.zoo.edu
Connected to rhino.zoo.edu.
Name (rhino:carol): csmith
Password:
ftp> cd work
ftp> dir
total 3
-rw-r--r--  1 csmith   mgmt    47 Feb  5  2001 for.ed
-rw-r--r--  1 csmith   mgmt   264 Oct 11 12:18 message
-rw-r--r--  1 csmith   mgmt   724 Nov 20 14:53 todo
ftp> get todo
local: todo remote: todo
227 Entering Passive Mode (17,254,16,11,224,18).
150 Opening BINARY mode data connection for todo (724 bytes)
226 Transfer complete.
724 bytes received in 00:00 (94.06 KB/s)
ftp> quit
$ ls
afile   ch2    somefile    todo

We've explored the most basic ftp commands here. Entering help at an ftp> prompt gives a list of all commands; entering help followed by an ftp command name gives a one-line summary of that command.

Pages: 1, 2, 3

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