Automating FTP on the Mac

There is no shortage of GUI FTP programs, but kicking it old school on the command line allows you to easily automate uploads and downloads. The best part is, there is nothing to install. Everything you need waits patiently behind the warm glow of a Terminal session.

The Mac Command Line FTP Program

The default command line FTP program in OS X 10.5 Leopard resides at /usr/bin/ftp

By all outward appearances and behavior, the Mac FTP program is the standard BSD version. The man page is the standard BSD main page and contains a wealth of useful information.

A typical command line FTP session is interactive and goes something like this:

  • login to an FTP server
  • issue commands (ls (list), get (download), put (upload))
  • quit

If you have a repetitive FTP task, the fun quickly fades into a mind numbing exercise. This is where FTP automation shines.

The Magical .netrc File

What makes FTP automation possible is a magical, little known file called .netrc. The .netrc file is a plain text file that is hidden (the file name starts with a period) and lives in the root of your home directory. The .netrc file allows FTP to perform automatic logins to FTP servers based on the name.

The .netrc is not created by default. You have to create it manually. To create an empty .netrc file, open a Terminal and use the following commands:

touch .netrc
chmod 700 .netrc

It is critical that you issue the chmod command to set the permissions so that only the owner of the file can view it. If the permissions are not set correctly, the FTP client will assume it has been compromised and will refuse to use it.

Inside the .netrc, you define a block of settings for each FTP server you use, including the machine name, the login ID, and the password. Here is a typical block for a mythical FTP server:

machine myftpserver.com
   login myuser
   password mypassword

There are additional settings that can be included. Check the FTP man page for more. You can test your settings by typing “ftp myftpserver.com” at a Terminal prompt, and it should automatically login. Note that you can store multiple FTP server logins in the .netrc file.

Sending FTP Commands from a BASH Shell Script

Once logins are automated, the final piece of the puzzle is to script a set of FTP commands. The following example uses an advanced BASH shell scripting technique called a “here” document to group the FTP commands to be sent to the server.

#!/bin/bash
/usr/bin/ftp -d myftpserver.com << ftpEOF
   prompt
   put "*.html"
   quit
ftpEOF

The FTP command is issued with the -d flag (debug mode) to make it more verbose. That makes any kind of error more obvious. The connection is made to myftpserver.com using the ID and password from the .netrc file. Once the connection is made, the rest of the commands are issued one at a time until the end of the “here” document at the second “ftpEOF”. Note that any valid FTP commands can be sent. In the example, the prompt command tells FTP not to prompt for multiple file operations, then the put uploads all files with an .html extension. If you want to go the extra mile, you can extend the shell script and do things like reconnect to the FTP server to verify the file sizes of your uploads.

While there are several ways you can automate FTP, the nice thing about this method is that it is portable to Linux or any other Unix system.

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