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Session initiation: sxhl

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{{short description|Computer protocol}}
{{More citations needed|date=December 2009}}

'''Files transferred over Shell protocol''' ('''FISH''') is a network [[Protocol (computing)|protocol]] that uses [[Secure Shell]] (SSH) or [[Remote Shell]] (RSH) to [[file transfer|transfer files]] between computers and manage remote files.

The advantage of FISH is that all it requires on the server-side is an SSH or RSH implementation, [[Unix shell]], and a set of standard [[Unix]] utilities (like [[ls]], [[cat (Unix)|cat]] or [[dd (Unix)|dd]]—unlike other methods of remote access to files via a remote shell, [[Secure copy|scp]] for example, which requires ''scp'' on the server side). Optionally, there can be a special FISH server program (called ''start_fish_server'') on the server, which executes FISH commands instead of Unix shell and thus speeds up operations.

The protocol was designed by Czech Linux Kernel Hacker, Pavel Machek, in 1998 for the [[Midnight Commander]] software tool.<ref>[https://github.com/MidnightCommander/mc/blob/master/src/vfs/fish/fish.c File: ''Fish.c'' - via Midnight Commander Official Repository]</ref>

== Protocol messages ==
Client sends text requests of the following form:

#FISH_COMMAND arguments...
equivalent shell commands,
which may be multi-line

Fish commands are all defined, shell equivalents may vary.
Fish commands always have priority: the server is expected to execute a fish command if it understands it. If it does not, however, it can try to execute a shell command.
When there is no special server program, Unix shell ignores the fish command as a comment and executes the equivalent shell command(s).

Server replies are multi-line, but always end with

### xyz<optional text>

line. <code>###</code> is a prefix to mark this line, <code>xyz</code> is the return code.
Return codes are a superset to those used in [[FTP]].
The codes 000 and 001 are special, their meaning depends on presence of server output before the end line.

== Session initiation ==
The client initiates SSH or RSH connection with {{code|echo FISH:;/bin/sh|fish}} as the command executed on remote machine. This should make it possible for the server to distinguish FISH connections from normal RSH or SSH.

The first two commands sent to the server are <code>FISH</code> and <code>VER</code> to negotiate FISH protocol, its version and extensions.
{{sxhl|2=fish|<nowiki/>
#FISH
echo; start_fish_server; echo '### 200'

#VER 0.0.2 <feature1> <feature2> <...>
echo '### 000'
}}
The server may reply to VER command with a lines like

VER 0.0.0 <feature2> <...>
### 200

which indicates supported version of the FISH protocol and supported extensions.

== Implementations ==
* [[Midnight Commander]]<ref>{{cite web | url=https://github.com/MidnightCommander/mc/blob/master/src/vfs/fish/fish.c | title=Mc/Fish.c at master · MidnightCommander/Mc | website=[[GitHub]] }}</ref>
* [[Far Manager#Linux, MacOS and BSD version|far2l]]<ref>{{cite web | url=https://github.com/elfmz/far2l/issues/1819 | title=Feature: Consider porting FISH(FIle transfer over SHell filesystem) from Midnight Commander · Issue #1819 · elfmz/Far2l | website=[[GitHub]] }}</ref>
* [[Lftp]]<ref>{{cite web | url=https://github.com/lavv17/lftp/blob/master/src/Fish.cc | title=LFTP/SRC/Fish.cc at master · lavv17/LFTP | website=[[GitHub]] }}</ref>
* fish:// [[KDE]] [[KIO|kioslave]]<ref>{{cite web | url=https://github.com/KDE/kio-extras/blob/master/fish/fish.cpp | title=Kio-extras/Fish/Fish.CPP at master · KDE/Kio-extras | website=[[GitHub]] }}</ref> (with [[konqueror]], [[Krusader]] or [[Dolphin (file manager)|Dolphin]])
* fish as [https://github.com/greyltc/tcl-vfs/blob/master/library/template/fishvfs.tcl tcl-vfs]
* FISH was implemented in [[Emacs]] TRAMP some time ago, but support was removed<ref>[https://github.com/emacs-mirror/emacs/commit/03c1ad4351c10ec998410e8d34f52ac4a1a0decd#diff-96ee1cf8a36451f16ddf3f468f6ac74643eeee171d17054ca0c8cbf6653a26a8 related commit in Emacs]</ref><ref>{{cite web | url=https://lists.gnu.org/archive/html/tramp-devel/2010-09/msg00001.html | title=Re: Tramp's fish method }}</ref> (although TRAMP still can use shell connections in a similar way using tramp-sh.el script file)

== See also ==
* [[SSHFS]]
* [[SSH File Transfer Protocol]]

==References==
{{Reflist}}

== External links ==
* [http://cvs.savannah.gnu.org/viewcvs/mc/mc/vfs/README.fish?view=markup README.fish from Midnight Commander]

{{DEFAULTSORT:Files Transferred Over Shell Protocol}}
[[Category:Network file transfer protocols]]

Files transferred over shell protocol - Revision history

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