How to automate your FTP session- Part-1

Hardly a day goes by without an FTP automation question appearing in the newsgroups. Until now, the stock answers (for Unix) have been as follows (the options for Windows are sparse indeed):

1. Pipe commands into FTP's standard input. This works great when it works, but doesn't allow for synchronization, error handling, decision making, and so on, and can get into an awful mess when something goes wrong. For example, some FTP clients do special tricks with the password that tend to thwart piping of standard input or "here" documents into them. Also, the exact syntax of your procedure depends on which shell (sh, ksh, csh, bash, etc) you are using. Also, your password can be visible to other people through "ps" or "w" listings.

2. Put the commands to be executed into the .netrc file in your login directory in the form of a macro definition. Except for avoiding shell syntax differences, this is not much different than the first option, since FTP commands don't have any capability for error detection, decision making, conditional execution, etc. Note that the .netrc file can also be used to store host access information (your username and password on each host). It's a glaring security risk to have this well-known file on your disk; anybody who gains access to your .netrc also gains access to all the hosts listed in it.

3. Use Expect to feed commands to the FTP prompt. This improves the situation with synchronization, but:

* It's cumbersome and error-prone, since it relies on the specific messages and prompts of each FTP client and server, which vary, rather than the FTP protocol itself, which is well-defined. Expect scripts break whenever the client or server prompts or text messages change, or if the messages come out in different languages.
* You're still stuck with same dumb old FTP client and its limited range of function.

4. Use FTP libraries available for Perl, Tcl, C, etc. This might give direct programmatic access to the FTP protocol, but still offers limited functionality unless you program it yourself at a relatively low and detailed level.