usr.bin/fetch/fetch.1

.\" $Id: fetch.1,v 1.29 1999/02/23 18:51:13 wollman Exp $
.Dd February 22, 1999
.Dt FETCH 1
.Os FreeBSD 4.0
.Sh NAME
.Nm fetch
.Nd retrieve a file by Uniform Resource Locator
.Sh SYNOPSIS
.Nm fetch
.Op Fl AMPablmnpqrtv
.Op Fl S Ar size
.Op Fl T Ar timeout
.Op Fl o Ar file
.Ar URL
.Op Ar ...
.Nm fetch
.Op Fl MPRlmnpqrv
.Op Fl S Ar size
.Op Fl o Ar file
.Op Fl c Ar dir
.Fl f Ar file
.Fl h Ar host
.Sh DESCRIPTION
.Nm fetch
allows a user to transfer files from a remote network site using
either the
.Tn FTP
or the
.Tn HTTP
protocol. In the first form of the command, the
.Ar URL
may be of the form
.Li http://site.domain/path/to/the/file
or
.Li ftp://site.domain/path/to/the/file .
To denote a local filename to be copied or linked to (see the
.Fl l
flag below), the
.Em file:/path/to/the/file
URL form is used.  See URL SYNTAX, below.
.Pp
The second form of the command can be used to get a file using the
.Tn FTP
protocol, specifying the file name and the remote host with the
.Fl h
and the
.Fl f
flags.
.Pp
The following options are available:
.Bl -tag -width Fl
.It Fl A
Do not automatically follow ``temporary'' (302) redirects.  Some
broken Web sites will return a redirect instead of a not-found error
when the requested object does not exist.
.It Fl a
Automatically retry the transfer upon soft failures.
.It Fl b
Work around a bug in some
.Tn HTTP
servers which fail to correctly implement the
.Tn TCP
protocol.
.It Fl c Ar dir
The file to retrieve is in directory
.Ar dir
on the remote host.
.It Fl f Ar file
The file to retrieve is named
.Ar file
on the remote host.
.It Fl h Ar host
The file to retrieve is located on the host
.Ar host .
.It Fl l
If target is a
.Ar file:/
style of URL, make a link to the target rather than trying
to copy it.
.It Fl M
.It Fl m
Mirror mode: Set the modification time of the file so that it is
identical to the modification time of the file at the remote host.
If the file already exists on the local host and is identical (as
gauged by size and modification time), no transfer is done.
.It Fl n
Don't preserve the modtime of the transferred file, use the current time.
.It Fl o Ar file
Set the output file name to
.Ar file .
By default, a ``pathname'' is extracted from the specified URI, and
its basename is used as the name of the output file.  A
.Ar file
argument of
.Sq Li \&-
indicates that results are to be directed to the standard output.
.It Fl P
.It Fl p
Use the passive mode of the
.Tn FTP
protocol.  This is useful for crossing certain sorts of firewalls.
.It Fl q
Quiet mode. Do not report transfer progress on the terminal.
.It Fl R
The filenames specified are ``precious'', and should not be deleted
under any circumstances, even if the transfer failed or was incomplete.
.It Fl r
Restart a previously interrupted transfer.
.It Fl S Ar bytes
Require the file size reported by
.Tn FTP
or
.Tn HTTP
server to match the value specified with this option.
On mismatch, a message is printed and the file will not be fetched.
If the server does not support reporting of file sizes, the option
will be ignored and the file will be retrieved anyway.
This option is useful to prevent
.Nm fetch
from downloading a file that is either incomplete or the wrong version,
given the correct size of the file in advance.
.It Fl s
Ask server for size of file in bytes and print it to stdout. Do not
actually fetch the file.
.It Fl T Ar seconds
Set timeout value to
.Ar seconds.
Overrides the environment variables
.Ev FTP_TIMEOUT
for ftp transfers or
.Ev HTTP_TIMEOUT
for http transfers if set.
.It Fl t
Work around a different set of buggy
.Tn TCP
implementations.
.It Fl v
Increase verbosity.  More
.Fl v Ns \&'s
result in more information.
.El
.Pp
Many options are also controlled solely by the environment (this is a
bug).
.Sh URL SYNTAX
.Nm
accepts
.Tn http
and
.Tn ftp
URL's, as described in RFC1738.  For
.Tn ftp
URL's, a username and password may be specified, using the syntax
.Li ftp://user:password@host/.
If the path is to be absolute, as opposed to relative to the user's
home directory, it must start with %2F, as in
.Li ftp://root:mypass@localhost/%2Fetc/passwd .
.Nm Fetch
condenses multiple slashes in an
.Tn ftp
URL into a single slash; literal multiple slashes translate to an
.Tn ftp
protocol error.
.Sh PROXY SERVERS
Many sites use application gateways (``proxy servers'') in their
firewalls in order to allow communication across the firewall using a
trusted protocol.  The
.Nm fetch
program can use both the
.Tn FTP
and the
.Tn HTTP
protocol with a proxy server.
.Tn FTP
proxy servers can only relay
.Tn FTP
requests;
.Tn HTTP
proxy servers can relay both
.Tn FTP
and
.Tn HTTP
requests.
A proxy server can be configured by defining an environment variable
named
.Dq Va PROTO Ns Ev _PROXY ,
where
.Va PROTO
is the name of the protocol in upper case.  The value of the
environment variable specifies a hostname, optionally followed by a
colon and a port number.
.Pp
The
.Tn FTP
proxy client passes the remote username, host and port as the
.Tn FTP
session's username, in the form
.Do Va remoteuser Ns Li \&@ Ns Va remotehost
.Op Li \&@ Ns Va port
.Dc .
The
.Tn HTTP
proxy client simply passes the originally-requested URI to the remote
server in an
.Tn HTTP
.Dq Li GET
request.  HTTP proxy authentication is not yet implemented.
.Sh HTTP AUTHENTICATION
The
.Tn HTTP
protocol includes support for various methods of authentication.
Currently, the
.Dq basic
method, which provides no security from packet-sniffing or
man-in-the-middle attacks, is the only method supported in
.Nm fetch .
Authentication is enabled by the
.Ev HTTP_AUTH
and
.Ev HTTP_PROXY_AUTH
environment variables.  Both variables have the same format, which
consists of space-separated list of parameter settings, where each
setting consists of a colon-separated list of parameters.  The first
two parameters are always the (case-insensitive) authentication scheme
name and the realm in which authentication is to be performed.  If the
realm is specified as
.Sq Li \&* ,
then it will match all realms not specified otherwise.
.Pp
The
.Li basic
authentication scheme uses two additional optional parameters; the
first is a user name, and the second is the password associated with
it.  If either the password or both parameters are not specified in
the environment, and the standard input of
.Nm
is connected to a terminal, then
.Nm
will prompt the user to enter the missing parameters.  Thus, if the
user is known as
.Dq Li jane
in the
.Dq Li WallyWorld
realm, and has a password of
.Dq Li QghiLx79
there, then she might set her
.Ev HTTP_AUTH
variable to:
.Bl -enum -offset indent
.It
.Dq Li basic:WallyWorld:jane:QghiLx79
.It
.Dq Li basic:WallyWorld:jane ,
or
.It
.Dq Li basic:WallyWorld
.El
.Pp
and
.Nm
will prompt for any missing information when it is required.  She might
also specify a realm of
.Dq Li \&*
instead of
.Dq Li WallyWorld
to indicate that the parameters can be applied to any realm.  (This is
most commonly used in a construction such as
.Dq Li basic:* ,
which indicates to
.Nm
that it may offer to do
.Li basic
authentication for any realm.
.Sh ERRORS
The
.Nm
command returns zero on success, or a non-zero value from
.Aq Pa sysexits.h
on failure.  If multiple URIs are given for retrieval,
.Nm
will attempt all of them and return zero only if all succeeded
(otherwise it will return the error from the last failure).
.Sh ENVIRONMENT
.Bl -tag -width FTP_PASSIVE_MODE -offset indent
.It Ev FTP_TIMEOUT
maximum time, in seconds, to wait before aborting an
.Tn FTP
connection.
.It Ev FTP_LOGIN
the login name used for
.Tn FTP
transfers (default
.Dq Li anonymous )
.It Ev FTP_PASSIVE_MODE
force the use of passive mode FTP
.It Ev FTP_PASSWORD
the password used for
.Tn FTP
transfers (default
.Dq Va yourname Ns Li \&@ Ns Va yourhost )
.It Ev FTP_PROXY
the address (in the form
.Do Va hostname Ns
.Op Li : Ns Va port
.Dc )
of a proxy server which understands
.Tn FTP
.It Ev HTTP_AUTH
defines authentication parameters for
.Tn HTTP
.It Ev HTTP_PROXY
the address (in the form
.Do Va hostname Ns
.Op Li : Ns Va port
.Dc )
of a proxy server which understands
.Tn HTTP
.It Ev HTTP_PROXY_AUTH
defines authentication parameters for
.Tn HTTP
proxy servers
.It Ev HTTP_TIMEOUT
maximum time, in seconds, to wait before aborting an
.Tn HTTP
connection.
.Sh SEE ALSO
.Xr ftp 1 ,
.Xr tftp 1
.Rs
.%A R. Fielding
.%A J. Gettys
.%A J. Mogul
.%A H. Frystyk
.%A T. Berners-Lee
.%T "Hypertext Transfer Protocol \-\- HTTP/1.1"
.%O RFC 2068
.%D January 1997
.Re
.Rs
.%A T. Berners-Lee
.%A L. Masinter
.%A M. McCahill
.%T "Uniform Resource Locators (URL)"
.%O RFC 1738
.%D December 1994
.Re
.Rs
.%A J. Postel
.%A J.K. Reynolds
.%T "File Transfer Protocol"
.%O RFC 959 / STD 9
.%D October 1985
.Re
.Rs
.%A M.R. Horton
.%T "Standard for interchange of USENET messages."
.%O RFC 850
.%D June 1983
.Re
.Sh HISTORY
The
.Nm fetch
command appeared in
.Fx 2.1.5 .
.Sh AUTHORS
The original implementation of
.Nm
was done by
.An Jean-Marc Zucconi .
It was extensively re-worked for
.Fx 2.2
by
.An Garrett Wollman .
.Sh BUGS
There are too many environment variables and command-line options.
.Pp
The
.Fl a
option is only implemented for certain kinds of
.Tn HTTP
failures, and no
.Tn FTP
failures.
.Pp
Only the
.Dq basic
authentication mode is implemented for
.Tn HTTP .
This should be replaced by digest authentication.
.Pp
Some
.Tn TCP
implementations (other than
.Tn FreeBSD )
fail to correctly implement cases where the
.Dv SYN
and/or
.Dv FIN
control flags are specified in packets which also contain data.
The
.Sq Fl t
flag works around the latter deficiency and the
.Sq Fl b
flag works around the former.  Since these are errors of the server's
.Tn TCP
stack, the best we can do is provide these workarounds.  Given a correct
server, an optimal
.Tn HTTP
transfer without
.Fl t
and
.Fl b
involves a minimum of two round trips (for small replies), one less than
other implementations.
.Pp
The
.Tn HTTP
standard requires interpretation of the
.Tn RFC 850
date format, which does not provide a century indication.  Versions of
.Nm fetch
prior to
.Fx 3.1
would interpret all such dates as being in the 1900s.  This version of
.Nm fetch
interprets such dates according to the rule given in
.Tn RFC 2068 :
.Bd -literal -offset indent
  o  HTTP/1.1 clients and caches should assume that an RFC-850 date
     which appears to be more than 50 years in the future is in fact
     in the past (this helps solve the "year 2000" problem).
.Ed