A LIST or NLST request asks the server to send the contents of a directory over the data connection already established by the client. The directory is identified by the current name prefix.
Normally the server responds with a mark using code 150. It then stops accepting new connections, attempts to send the contents of the directory over the data connection, and closes the data connection. Finally it
The server may reject the LIST or NLST request (with code 450 or 550) without first responding with a mark. In this case the server does not touch the data connection.
A directory is a list of files. It typically includes a name, type, size, and modification time of each file. The difference between LIST and NLST is that NLST returns a compressed form of the directory, showing only the name of each file, while LIST returns the entire directory.
The NLST format consists of a sequence of abbreviated pathnames. Each pathname is
\015\012 ASCII Code, without regard to the current binary flag. If an abbreviated
pathname starts with a slash, it represents the pathname obtained by replacing each
\012. If an abbreviated pathname does not start with a slash, it represents the
pathname obtained by concatenating
\012. For example, if a directory /pub produces
foo\015\012bar\015\012under NLST, it refers to the pathnames /pub/fo and /pub/bar.
The LIST format varies widely from server to server. The most common format is /bin/ls (UNIX) format, which is difficult to parse with even moderate reliability. This poses a serious problem for clients that need more information than names.
LIST and NLST have an optional parameter giving an encoded pathname of a file. The file may be either a directory or a regular file.
If the file is a regular file, the server provides information about that file, in the
same format as a single directory entry. However, if the file is a directory, most
servers will provide the contents of the directory, rather than information about the
directory. If the client says NLST x, for example, and the response is x
x could be a directory containing one file x, or it could be a regular file; the client
can't tell. This inconsistency makes LIST and NLST parameters useless for most
I recommend that servers always respond to a nonempty LIST parameter with information about the file, whether the file is a regular file or a directory; this is helpful for some types of indexing clients. I also recommend that servers reject NLST for regular files, and always respond to NLST with directory contents.
Beware that some servers use abbreviated names relative to the current name prefix, instead of the specified directory. I recommend against this behavior.