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