Sets the ports to use for FTP.
Value The port string. ""
Possible encoding names: ANSI, Arabic-Mac, Arabic-Win, Baltic-Win, CentralEurope-Mac, ChineseSimp-Mac, ChineseSimp-Win, ChineseTrad-Mac, ChineseTrad-Win, Cyrillic-Mac, Cyrillic-Win, EasternEurope-Win, Greek-Mac, Greek-Win, Hebrew-Mac, Hebrew-Win, ISO-8859-1, ISO-8859-2, ISO-8859-3, ISO-8859-4, ISO-8859-5, ISO-8859-6, ISO-8859-7, ISO-8859-8, ISO-8859-9, ISO-8859-15, Korean-Johab, Korean-Mac, Korean-Win, Latin1, Mac, Native, ShiftJIS-Mac, ShiftJIS-Win, Turkish-Mac, Turkish-Win, UTF-8, DOS or Windows. Pass native to use the native encoding of the current platform. "UTF-8"
It will be used to get the IP address to use for the FTP PORT instruction. The PORT instruction tells the remote server to connect to our specified IP address. The string may be a plain IP address, a host name, a network interface name (under Unix) or just a '-' symbol to let the library use your system's default IP address. Default FTP operations are passive, and thus won't use PORT.
You disable PORT again and go back to using the passive version by setting this option to empty string.
See also FTPPORT option in CURL manual.