The commands, from client to server, and replies, from server to client, are sent across the control connection is 7-bit
ASCII format. Like HTTP commands, FTP commands are readable by poeple. In order to delineate successive commands,
a carraigae return and line feed end each command. Each command consists of four uppercase ASCII characters, some with
optional arguments.
Some of the most common commands are:
- USER username: Used to sent the user identifiaction to the server.
- PASS password: U:sed to sent the user password to the servver.
- LIST: Used to ask the user to send back a list of all the files in the current remote directory.
- RETR filename: Used to retrieve a file from the current directoryof the remote host.
- STOR filename: Used to store a file into the current directory of the remote host.
There is typically a one-to-one correspondence between the command that hthe suer issue and the FTP command sent across
the control connection. Each command is followed by a reply, sent from server to client. The replies are three-digit
numbers, with optional message following the number. This is similar in structure to the status code and phrase in the
status line of the HTTP response mseeage; the inventors of HTTP intnetionally included this similarity in the HTTP response
message.
