The following commands are recognized(* =>'s unimplemented):

USER PORT RETR MSND* ALLO DELE SITE* XMKD CDUP

PASS PASV STOR MSOM* REST* CWD STAT* RMD XCUP

ACCT* TYPE APPE MSAM* RNFR XCWD HELP XRMD STOU

REIN* STRU MLFL* MRSQ* RNTO LIST NOOP PWD

QUIT MODE MAIL* MRCP* ABOR NLST MKD XPWD

AUTH ADAT PROT PBSZ MIC ENC CCC

The commands and replies are sent via the control connection, and are in NVT ASCII. The commands are 3 to 4 bytes of uppercase ASCII, and to some of them there is optional argument. Here are the meanings of some commonly used FTP commands:

*USER* <username>	Identifies the user attempting to establish an FTP session.
*PASS*<password>	Specifies the password for the user given previously by the USER command.
*QUIT*	Terminates the FTP session and closes the control connection.
*PORT* <n1,n2,n3,n4,n5,n6>	Client IP address (n1,n2,n3,n4) and port (n5 x 256 +n6).
*PASV*	Requests that the FTP server allow the User-DTP to initiate passive data connections.
*TYPE* <type>	Specifies for the file to be transferred the data type (ASCII, EBCDIC, Image or Local), and optionally the format control (Non Print, Telnet or Carriage Control).
*RETR*	Tells the server to send the user a file.
*STOR*	Sends a file to the server.
*SYST*	Requests that the server return the system type

BSD Interface

The FTP RFC specifies how the user PI (protocol interpreter) communicates with the server PI, but does not specify the user interface. Most vendors use the BSD (Berkeley Software Distribution) interface.

The BSD interface for FTP support the following commands:

Commands may be abbreviated.

!

delete

mdelete

proxy

runique

$

debug

mdir

sendport

send

account

dir

mget

put

size

append

disconnect

mkdir

pwd

status

ascii

form

mls

quit

struct

bell

get

mode

quote

sunique

binary

glob

modtime

recv

system

bye

hash

mput

remotehelp

tenex

case

help

nmap

rstatus

trace

cd

image

nlist

rhelp

type

cdup

lcd

ntrans

rename

user

close

ls

open

reset

verbose

cr

macdef

prompt

rmdir

?

clear

private

protect

safe

Though the number of commands is high, the use of them is not as complicated as one might think. First of all because lots of the commands are rarely being used if at all, for example the command "tenex" - TENEX is an operating system with a different file representation then UNIX, and the command "tenex" was needed to invoke translation. Now TENEX is no longer is use, and the command as well. Also, because of the ability of FTP to handle different representations of text files, some commands are needed to specify the representation that is in use in the other side of the connection, so translation will be possible. And finally, some of the commands in BSD interface are exactly identical, such as "bye" and "quit" (to logoff from server) or "help" and "?" (to show the list of available commands.

Here are the meanings of commonly used commands in BSD interface:

?	to request help or information about the FTP commands
ascii	to set the mode of file transfer to ASCII (this is the default and transmits seven bits per character)
binary	to set the mode of file transfer to binary (the binary mode transmits all eight bits per byte and thus provides less chance of a transmission error and must be used to transmit files other than ASCII files)
bye	to exit the FTP environment (same as quit )
cd	to change directory on the remote machine
close	to terminate a connection with another computer
	close brubeck	closes the current FTP connection with brubeck , but still leaves you within the FTP environment.
delete	to delete (remove) a file in the current remote directory (same as rm in UNIX)
get	to copy one file from the remote machine to the local machine
	get ABC DEF	copies file ABC in the current remote directory to (or on top of) a file named DEF in your current local directory.
	get ABC	copies file ABC in the current remote directory to (or on top of) a file with the same name, ABC , in your current local directory.
help	to request a list of all available FTP commands
lcd	to change directory on your local machine (same as UNIX cd )
ls	to list the names of the files in the current remote directory
mkdir	to make a new directory within the current remote directory
mget	to copy multiple files from the remote machine to the local machine; you are prompted for a y / n answer before transferring each file
	mget *	copies all the files in the current remote directory to your current local directory, using the same filenames. Notice the use of the wild card character, * .
mput	to copy multiple files from the local machine to the remote machine; you are prompted for a y / n answer before transferring each file
open	to open a connection with another computer
	open brubeck	opens a new FTP connection with brubeck ; you must enter a username and password for a brubeck account (unless it is to be an anonymous connection).
put	to copy one file from the local machine to the remote machine
pwd	to find out the pathname of the current directory on the remote machine
quit	to exit the FTP environment (same as bye )
rmdir	to to remove (delete) a directory in the current remote directory

For more information check:

http://unixhelp.ed.ac.uk/CGI/man-cgi?ftp

http://www.networksorcery.com/enp/rfc/rfc959.txt