fish-shell/doc_src/doc.hdr

/** \mainpage Fish user documentation

\section introduction The friendly interactive shell

This is the documentation for \c fish, the friendly interactive
shell. \c fish is a user friendly commandline shell shell intended
mostly for interactive use. A shell is a program used to execute other
programs. For the latest information on \c fish, please visit the <a
href="http://roo.no-ip.org/fish/"><tt>fish</tt> homepage</a>.

\section syntax Syntax overview

Shells like fish are used by giving them commands. Every \c fish
command follows the same simple syntax.

A command is executed by writing the name of the command followed by
any arguments.

Example:

<tt>echo hello world</tt>

calls the \c echo command. \c echo is a command which will write its
arguments to the screen. In the example above, the output will be
'hello world'. Everything in fish is done with commands. There are
commonds for performing a set of command multiple times, commands for
assigning variables, commands for treating a group of commands as a
single command, etc.. And every single command follows the same simple
syntax.

If you wish to find out more about the echo command used above, read
the manual page for the echo command by writing:

<tt>man echo</tt>

\c man is a command for displaying a manual page on a given
topic. There are manual pages for almost every command on most
computers. There are also manual pages for many other things, such as
system libraries and important files.

Every program on a computer can be used as a command in \c fish. If
the program file is located in one of the directories in the <a
href="#variables-special">PATH</a>, it is sufficient to type the name
of the program to use it. Otherwise the whole filename, including the
directory (like \c /home/me/code/checkers/checkers or \c ../checkers)
has to be used.

Here is a list of some useful commands:

- \c cd, change the current directory
- \c ls, list the contents of a directory
- \c man, print a manual page
- \c mv, move files
- \c cp, copy files
- \c open, open files with the default application associated with each filetype
- \c less, read the contents of files 

Commands and parameters are separated by the space character
(&nbsp;). Every command ends with either a newline (i.e. by pressing
the return key) or a semicolon (;). More than one command can be
written on the same line by separating them with semicolons.


\subsection quotes Quotes

Sometimes features such as <a href="#globbing">parameter expansion</a>
and <a href="#escapes">character escapes</a> get in the way. When that
happens, the user can write a parameter within quotes, either '
(single quote) or " (double quote). There is one important difference
between single quoted and double quoted strings: When using double
quoted string, <a href='#expand-variable'>variable expansion</a> still
takes place.  Other than that, a quoted parameter will not be
parameter expanded, may contain spaces, and escape sequences are
ignored. Single quotes have no special meaning withing double quotes
and vice versa.

Example:

<tt>rm "cumbersome filename.txt"</tt>

Will remove the file 'cumbersome filename.txt'.

\subsection escapes Escaping characters

Some characters can not be written directly on the command line. For
these characters, so called escape sequences are provided. These are:

- <tt>'\\n'</tt>, escapes a newline character
- <tt>'\\t'</tt>, escapes the tab character
- <tt>'\\b'</tt>, escapes the backspace character
- <tt>'\\r'</tt>, escapes the carriage return character
- <tt>'\\e'</tt>, escapes the escape character
- <tt>'\\ '</tt>, escapes the space character
- <tt>'\\$'</tt>, escapes the dollar character
- <tt>'\\\\'</tt>, escapes the backslash character
- <tt>'\\*'</tt>, escapes the star character
- <tt>'\\?'</tt>, escapes the question mark character
- <tt>'\\~'</tt>, escapes the tilde character
- <tt>'\\#'</tt>, escapes the hash character
- <tt>'\\('</tt>, escapes the left parenthesis character
- <tt>'\\)'</tt>, escapes the right parenthesis character
- <tt>'\\{'</tt>, escapes the left curly bracket character
- <tt>'\\}'</tt>, escapes the right curly bracket character
- <tt>'\\['</tt>, escapes the left bracket character
- <tt>'\\]'</tt>, escapes the right bracket character
- <tt>'\\\<'</tt>, escapes the less than character
- <tt>'\\\>'</tt>, escapes the more than character
- <tt>'\\^'</tt>, escapes the circumflex character
- <tt>'\\x<i>xx</i>'</tt>, where <tt><i>xx</i></tt> is a hexadecimal number, escapes the ascii character with the specified value
- <tt>'\\o<i>ooo</i>'</tt>, where <tt><i>ooo</i></tt> is an octal number, escapes the ascii character with the specified value
- <tt>'\\u<i>xxxx</i>'</tt>, where <tt><i>xxxx</i></tt> is a hexadecimal number, escapes the 16-bit unicode character with the specified value
- <tt>'\\U<i>xxxxxxxx</i>'</tt>, where <tt><i>xxxxxxxx</i></tt> is a hexadecimal number, escapes the 32-bit unicode character with the specified value

\subsection redirects IO redirection

Most program use three types of input/output (IO), each represented by
a number called a file descriptor (FD). These are:

- Standard input, FD 0, for reading, defaults to reading from the keyboard. 
- Standard output, FD 1, for writing, defaults to writing to the screen.
- Standard error, FD 2, for writing errors and warnings, defaults to writing to the screen.

The reason for providing for two methods of output is so errors and
warnings can be separated from regular program output.

Any file descriptor can be directed to a different output than it's
default through a simple mechanism called a redirecton.

An example of a file redirection is <tt> echo hello \>output.txt</tt>,
which directs the output of the echo command to the file error.txt.

- To redirect standard input, write <tt>\<SOURCE_FILE</tt> 
- To redirect standard output, write <tt>\>DESTINATION</tt> 
- To redirect standard error, write <tt>^DESTINATION</tt> 
- To redirect standard output to a file which will be appended, write <tt>\>\>DESTINATION_FILE</tt>
- To redirect standard error to a file which will be appended, write <tt>^^DESTINATION_FILE</tt> 

<tt>DESTINATION</tt> can be one of the following: 

- A filename. The output will be written to the specified file.
- An ampersand (\&) followed by the number of a file descriptor. The file descriptor will be a duplicate of the specified file descriptor.
- A minus sign (-). The FD will be closed.

Example:

To redirect both standard output and standard error to the file
all_output.txt, you can write <tt>echo Hello \>all_output.txt
^\&1</tt>.

Any FD can be redirected in an arbitrary way by prefixing the
redirection with the number of the FD.

- To redirect input of FD number N, write <tt>N\<DESTINATION</tt>
- To redirect output of FD number N, write <tt>N\>DESTINATION</tt> 
- To redirect output of FD number N to a file which will be appended, write <tt>N\>\>DESTINATION_FILE</tt>

Example: <tt>echo Hello 2\>-</tt> and <tt>echo Hello ^-</tt> are
equivalent.

\subsection piping Piping

The user can string together multiple commands into a so called
pipeline. This means that the standard output of one command will be read
in as standard input into the next command. This is done by separating
the commands by the pipe character (|). For example

<tt>cat foo.txt | head</tt>

will call the 'cat' program with the parameter 'foo.txt', which will
print the contents of the file 'foo.txt'. The contents of foo.txt will
then be filtered through the program 'head', which will pass on the
first ten lines of the file to the screen. For more information on how
to combine commands through pipes, read the manual pages of the
commands you want to use using the 'man' command. If you want to find
out more about the 'cat' program, type <tt>man cat</tt>.

Pipes usually connect file descriptor 1 (standard output) of the first
process to file descriptor 0 (standard input) of the second
process. It is possible use a different output file descriptor by
prepending the desired FD number and then output redirect symbol to
the pipe. For example:

<tt>make fish 2>|less</tt>

will attempt to build the fish program, and any errors will be shown
using the less pager.

\subsection syntax-background Background jobs

When you start a job in \c fish, \c fish itself will pause, and give
control of the terminal to the program just started. Sometimes, you
want to continue using the commandline, and have the job run in the
background. To create a background job, append a \& (ampersand) to
your command. This will tell fish to run the job in the background.

\subsection syntax-job-control Job control


Most programs allow you to suspend the programs execution and return
control to \c fish by Pressing ^Z (Press and hold the Control key and
press 'z'). Once back at the \c fish commandline, you can start other
programs and do anything you want. If you then want to go back to the
suspended command by using the <a href="builtins.html#fg">fg</a>
command.

If you instead want to put a suspended job into the foreground, use
the <a href="builtins.html#fg">fg</a> command.

To get a listing of all currently started jobs, use the <a
href="builtins.html#jobs">jobs</a> command.


\subsection syntax-words Some common words

This is a short explanation of some of the commonly used words in fish.

- argument, a parameter given to a command
- builtin, a command that is implemented as part of the shell
- command, a program
- function, a block of one or more fish commands that can be called as a single command. By using functions, it is possible to string together multiple smaller commands into one more advanced command.
- job, a running pipeline or command
- pipeline, a set of commands stringed together so that the output of one command is the input of the next command
- redirection, a operation that changes one of the input/output streams associated with a job

\section help Help

\c fish has an extensive help system. Use the <a
href="commands.html#help"><tt>help</tt></a> command to obtain help on
a specific subject or command. For instance, writing <tt>help
syntax</tt> displays the <a href="#syntax">syntax section</a> of this
documentation.

Help on a specific builtin can also be obtained with the <tt>-h</tt>
parameter. For instance, to obtain help on the \c fg builtin, either
type <tt>fg -h</tt> or <tt>help fg</tt>.


\section completion Tab completion

Tab completion is one of the most time saving features of any modern
shell. By tapping the tab key, the user asks \c fish to guess the rest
of the command or parameter that the user is currently typing. If
there is only one possible completion, \c fish will write it out. If
there is more than one completion, \c fish will write out the longest
common prefix that all completions have in common. If all completions
differ on the first character, a list of all possible completions is
printed. The list features descriptions of the completions and if the
list doesn't fit the screen, it is scrollable by using the arrow keys,
the page up/page down keys or the space bar. Press any other key will
exit the list and insert the presssed key into the command line.

These are the general purpose tab completions that \c fish provides:

- Completion of commands, both builtins, functions and regular programs.
- Completion of environment variable names.
- Completion of usernames for tilde expansion.
- Completion of filenames, even on strings with wildcards such as '*' and '?'.
- Completion of job id, job name and process names for <a href="#expand-process">process expansion</a>.

\c fish provides a large number of program specific completions. Most
of these completions are simple options like the \c -l option for \c
ls, but some are more advanced. The latter include:

- The programs 'man' and 'whatis' complete using all installed 
manual pages.
- The 'make' program complete using all targets in the Makefile in 
the current directory.
- The 'mount' command complete using all mount points specified in fstab.
- The 'ssh' command complete using all hosts in that are stored 
in the known_hosts file. (see the ssh documentation for more information) 
- The 'su' command complete using all users on the system
- The \c apt-get, \c rpm and \c tym commands complete using all installed packages.

\subsection completion-own Writing your own completions

Specifying your own completions is not complicated. To specify a
completion, one simply uses the \c complete command. \c complete takes
as a parameter the name of the command to specify a completion
for. For example, to add a completion for the program \c myprog, one
would start the completion command with <tt>complete -c myprog
...</tt>. To provide a list of possible completions for myprog, use
the \c -a switch. If \c myprog accepts the arguments start and stop,
this can be specified as <tt>complete -c myprog -a 'start
stop'</tt>. The argument to the \c -a switch is always a single
string. At completion time, it will be tokenized on spaces and tabs,
and variable expansion, command substitution and other forms of
parameter expansion will take place. 

Fish has a special syntax to support specifying switches accepted by a
command. The switches \c -s, \c -l and \c -o are used to specify a
short switch (single character, such as -l), a gnu style long switch (such as
--color) and an old-style long switch (like -shuffle),
respectively. If the command 'myprog' has an option '-o' which can
also be written as '--output', and which can take an additional value
of either 'yes' or 'no', this can be specified by writing:

<tt>complete -c myprog -s o -l output -a "yes no"</tt>

There are also special switches for specifying that a switch requires
an argument, to disable filename completion, to create completions
that are only available in some combinations, etc..  For a complete
description of the various switches accepted by the \c complete
command, see the documentation for the <a
href="builtins.html#complete">complete</a> builtin, or write 'complete
--help' inside the \c fish shell.

For examples of how to write your own complex completions, study the
completions in /etc/fish.d/completions (or ~/etc/fish.d/completions if
you installed fish in your home directory).

If you wish to use a completion, you should consider adding it to your
startup files. When completion has been requested for a command \c
COMMAND, fish will automatically look for the file
~/.fish.d/completions/COMMAND.fish. If it exists, it will be
automatically loaded. If you have written new completions for a common
Unix command, please consider sharing your work by sending it to <a
href='mailto: fish-users@lists.sf.net'>the fish mailinglist</a>.

\section expand Parameter expansion (Globbing)

When an argument for a program is given on the commandline, it
undergoes the process of parameter expansion before it is sent on to
the command.  There are many ways in which the user can specify a
parameter to be expanded. These include:

\subsection expand-wildcard Wildcards 

If a star (*) or a question mark (?) is present in the parameter, \c
fish attempts to mach the given parameter to any files in such a
way that '?' can match any character except '/' and '*' can match any
string of characters not containing '/'.

Example:
<code>a*</code> matches any files beginning with an 'a' in the current directory.

<code>???</code> matches any file in the current directory whose name is exactly three characters long.

If no matches are founf for a specific wildcard, it will expand intto
zero arguments, i.e. to nothing. If none of the wildcarded arguments
sent to a command result in any matches, the command will not be
executed. If this happens when using the shell interactively, a
warning will also be printed.

\subsection expand-command-substitution Command substitution

If a parameter contains a set of parenthesis, the text enclosed by the
parentesis will be interpreted as a list of commands. Om expansion,
this list is executed, and substituted by the output. If the output is
more than one line long, each line will be expanded to a new
parameter.

Example:

The command <code>echo (basename image.jpg .jpg).png</code> will
output 'image.png'.

The command <tt>for i in *.jpg; convert $i (basename $i .jpg).png;
end</tt> will convert all Jpeg files in the current directory to the
PNG format.


\subsection expand-brace Brace expansion

A comma separated list of characters enclosed en curly braces will be
expanded so each element of the list becomes a new parameter.

Example:

<tt>echo input.{c,h,txt}</tt> outputs 'input.c input.h input.txt'

The command <tt>mv *.{c,h} src/</tt> moves all files with the suffix
'.c' or '.h' to the subdirectory src.

\subsection expand-variable Variable expansion

A dollar sign followed by a string of characters is expanded into the
value of the environment variable with the same name. For an
introduction to the concept of environment variables, read the <a
href="#variables"> Environment variables</a> section.

Example:

<tt> echo \$HOME</tt> prints the home directory of the current
user. 

If you wish to combine environment variables with text, you can
encase the variables within braces to embed a variable inside running
text like <tt>echo Konnichiwa {$USER}san</tt>, which will print a
personalized Japanese greeting.

The {$USER}san syntax might need a bit of an elaboration.  Posix
shells allow you to specify a variable name using '$VARNAME' or
'${VARNAME}'. Fish only supports the former, but has no support
whatsoever for the latter or anything remotely like it. So what is
'{$VARNAME}' then? Well, '{WHATEVER}' is <a href='#brace'>brace
expansion</a>, the same as supported by Posix shells, i.e.  'a{b,c}d'
-> 'abd acd' works both in bash and on fish. So '{$VARNAME}' is a
bracket-expansion with only a single element, i.e.  it becomes
expanded to '$VARNAME', which will be variable expanded to the value
of the variable 'VARNAME'. So you might think that the brackets don't
actually do anything, and that is nearly the truth. The snag is that
there once along the way was a '}' in there somewhere, and } is not a
valid character in a variable name.  So anything after the otherwise
pointless bracket expansion becomes NOT a part of the variable name,
even if it happens to be a legal variable name character. That's why
'{$USER}san' works. A case of one syntax just lending itself so nicely
to solving an unrelated problem in it's spare time.

Variable expansion is the only type of expansion performed on double
quoted strings. There is, however, an important difference in how
variables are expanded when quoted and when unquoted. An unquoted
variable expansion will result in a variable number of arguments. For
example, if the variable $foo has zero elements or is undefined, the
argument $foo will expand to zero elements. If the variable $foo is an
array of five elements, the argument $foo will expand to five
elements. When quoted, like "$foo", a variable expansion will always
result in exactly one argument. Undefined variables will expand to the
empty string, and array variables will be concatenated using the space
character.


\subsection expand-home Home directory expansion

The ~ (tilde) character at the beginning of a parameter, followed by a
username, is expanded into the home directory of the specified user. A
lone ~, or a ~ followed by a slash, is expanded into the home
directory of the process owner.

\subsection expand-process Process expansion

The \% (percent) character at the beginning of a parameter followed by
a string is expanded into a process id. The following expansions are
performed:

- If the string is the entire word \c self, the shells pid is the result
- Otherwise, if the string is the id of a job, the result is the process
group id of the job.
- Otherwise, if any child processes match the specified string, their 
pids are the result of the expansion. 
- Otherwise, if any processes owned by the user match the specified 
string, their pids are the result of the expansion.

This form of expansion is useful for commands like kill and fg, which
take the process ids as an argument.

Example:

<tt>fg \%ema</tt> will search for a process whose command line begins
with the letters 'ema', such as emacs, and if found, put it in the
foreground.

<tt>kill -s SIGINT \%3</tt> will send the SIGINT signal to the job
with job id 3.

\subsection  combine Combining different expansions

All of the above expansions can be combined. If several expansions
result in more than one parameter, all possible combinations are
created.

Example:

If the current directory contains the files 'foo' and 'bar', the command
<tt>echo a(ls){1,2,3} </tt>
will output 'abar1 abar2 abar3 afoo1 afoo2 afoo3'.


\section variables Environment variables

The concept of environment variables are central to any
shell. Environment variables are variables, whose values can be set
and used by the user. For information on how to use the current value
of a variable, see the section on <a href='#expand-variable'>variable
expansion</a>.

To set a variable value, use the <a href="builtins.html#set"> \c set
command</a>.

Example: 

To set the variable \c smurf to the value \c blue, use the command
<tt>set smurf blue</tt>.

After a variable has been set, you can use the value of a variable in
the shell through <a href="expand-variable">variable expansion</a>.

Example:

To use the value of a the variable \c smurf, write $ (dollar synbol)
followed by the name of the variable, like <tt>echo Smurfs are
$smurf</tt>, which would print the result 'Smurfs are blue'.

\subsection variables-scope Variable scope

There are three kinds of variables in fish, universal, global and
local variables. Universal variables are shared between all fish
sessions a user is running on one computer. Global variables are
specific to the current fish session, but are not associated with any
soecific block scope, and will never be erased unless the user
explicitly requests it using <tt>set -e</tt>. Local variables are
specific to the current fish session, and associated with a specific
block of commands, and is automatically erased when a specific block
goes out of scope. A block of commands is a series of commands that
begins with one of the commands \c 'for, \c 'while' , \c 'if', \c
'function', \c 'begin' or \c 'switch', and ends with the command \c
'end'. The user can specify that a variable should have either global
or local scope using the \c -g/--global or \c -l/--local switches.

Variables can be explicitly set to be universal with the \c -U or \c
--universal switch, global with the \c -g or \c --global switch, or
local with the \c -l or \c --local switch.  The scoping rules when
creating or updating a variable are:

-# If a variable is explicitly set to either universal, global or local, that setting will be honored
-# If a variable is not explicitly set to be either universal, global or local, but has been previously defined, the variable scope is not changed
-# If a variable is not explicitly set to be either universal, global or local and has never befor been defined, the variable will be local to the currently executing functions. If no function is executing, the variable will be global.

There may be many variables with the same name, but different scopes.
When using a variable, the variable scope will be searched from the
inside out, i.e. a local variable will be used rather than a global
variable with the same name, a global variable will be used rather
than a universal variable with the same name.

Example:

The following code will not output anything:
<pre>
begin
	# This is a nice local scope where all variables will die
	set -l pirate 'There be treasure in them thar hills'
end

# This will not output anything, since the pirate was local
echo $pirate
</pre>

\subsection variables-universal More on universal variables

Universal variables are variables that are shared between all the
users fish sessions on the computer. Fish stores many of it's
configuration options as universal variables. This means that in order
to change fish settings, all you have to do is change the variable
value once, and it will be automatically updated for all sessions, and
preserved across computer reboots and login/logout.

To see universal variables in action, start two fish sessions side by
side, and issue the following command in one of them <tt>set
fish_color_cwd blue</tt>. Since \c fish_color_cwd is a universal
variable, the color of the current working directory listing in the
prompt will instantly change to blue on both terminals.

\subsection variables-functions Variable scope for functions

When calling a function, all non-global variables temporarily
dissapear. This shadowing of the local scope is needed since the
variable namespace would become cluttered, making it very easy to
accidentaly overwrite variables from another function.

For example, the following code will output 'Avast, mateys':

<pre>
function shiver
	set phrase 'Shiver me timbers'
end

function avast
	set phrase 'Avast, mateys'

	# Calling the shiver function here can not change any variables
	# in the local scope
	shiver

	echo $phrase
end

avast
</pre>

\subsection variables-export Exporting variables

Variables in fish can be exported. This means the variable will be
inherited by any commands started by fish. It is convention that
exported variables are in uppercase and unexported variables are in
lowercase.

Variables can be explicitly set to be exported with the \c -x or \c
--export switch, or not exported with the \c -u or \c --unexport
switch.  The exporting rules when creating or updating a variable are
identical to the scoping rules for variables:

-# If a variable is explicitly set to either be exported or not exported, that setting will be honored
-# If a variable is not explicitly set to be exported or not exported, but has been previously defined, the previous exporting rule for the variable is kept
-# If a variable is not explicitly set to be either global or local and has never befor been defined, the variable will not be exported


\subsection variables-arrays Arrays

\c fish can store a list of multiple strings inside of a variable. To
access one element of an array, use the index of the element inside of
square brackets, like this:

<pre>
echo $PATH[3]
</pre>

If you do not use any brackets, all the elements of the array will be
written as separate items. This means you can easily iterate over an
array using this syntax:

<pre>
for i in $PATH; echo $i is in the path; end
</pre>

To create a variable \c smurf, containing the items \c blue and \c
small, simply write:

<pre>
set smurf blue small
</pre>

It is also possible to set or erase individual elements of an array:

<pre>
\#Set smurf to be an array with the elements 'blue' and 'small'
set smurf blue small

\#Change the second element of smurf to 'evil'
set smurf[2] evil

\#Erase the first element
set -e smurf[1]

\#Output 'evil'
echo $smurf
</pre>

\subsection variables-special Special variables

The user can change the settings of \c fish by changing the values of
certain environment variables. 

- \c BROWSER, which is the users preferred web browser. If this variable is set, fish will use the specified browser instead of the system default browser to display the fish documentation.
- \c CDPATH, which is an array of directories in which to search for the new directory for the \c cd builtin.
- \c fish_color_normal, \c fish_color_command, \c fish_color_substitution, \c fish_color_redirection, \c fish_color_end, \c fish_color_error, \c fish_color_param, \c fish_color_comment, \c fish_color_match, \c fish_color_search_match, \c fish_color_cwd, \c fish_pager_color_prefix, \c fish_pager_color_completion, \c fish_pager_color_description and \c fish_pager_color_progress are used to change the color of various elements in \c fish. These variables are universal, i.e. when changing them, their new value will be used by all running fish sessions. The new value will also be retained when restarting fish.
- \c PATH, which is an array of directories in which to search for commands
- \c umask, which is the current file creation mask. The prefered way to change the umask variable is through the <a href="commands.html#umask">umask shellscript function</a>. An attempt to set umask to an invalid value will always fail.

\c fish also sends additional information to the user through the
values of certain environment variables. The user can not change the
values of these variables. They are:

- \c _, which is the name of the currently running command.
- \c history, which is an array containing the last commands that where entered.
- \c HOME, which is the users home directory. This variable can only be changed by the root user.
- \c PWD, which is the current working directory. 
- \c status, which is the exit status of the last foreground job to exit. If a job contains pipelines, the status of the last command in the pipeline is the status for the job.
- \c USER, which is the username. This variable can only be changed by the root user.

Variables whose name are in uppercase are exported to the commands
started by fish. This rule is not enfored by fish, but it is good
coding practice to use casing to distinguish between exported and
unexported variables. \c fish also uses several variables
internally. Such variables are prefixed with the string __FISH or
__fish. These should be ignored by the user.

\section builtin-overview Builtins 

Many other shells have a large library of builtin commands. Most of
these commands are also available as standalone commands, but have
been implemented in the shell anyway for whatever reason. To avoid
code duplication, and to avoid the confusion of subtly differing
versions of the same command, \c fish only implementing builtins for
actions which cannot be performed by a regular command.

\section bundle Commands bundled with fish 

The following commands are distributed with fish. Many of them are
builtins or shellscript functions, and can only be used inside fish.

- <a href="builtins.html#source">.</a>, read and execute the commands in a file 
- <a href="builtins.html#bg">bg</a>, set a command to the background
- <a href="builtins.html#begin">begin</a>, execute a block of commands
- <a href="builtins.html#bind">bind</a>, change keyboard bindings
- <a href="builtins.html#break">break</a>, stop the execution of a loop
- <a href="builtins.html#builtin">builtin</a>, execute a builtin command
- <a href="builtins.html#case">case</a>, conditionally execute a block of commands
- <a href="builtins.html#cd">cd</a>, change the current directory
- <a href="builtins.html#command">command</a>, execute an external program
- <a href="builtins.html#commandline">commandline</a>, set or get the contents of the commandline buffer
- <a href="builtins.html#complete">complete</a>, add and remove completions
- <a href="builtins.html#continue">continue</a>, skip the rest of the current lap of a loop
- <a href="commands.html#count">count</a>, count the number of arguments
- <a href="commands.html#dirh">dirh</a>, view the directory history
- <a href="commands.html#dirs">dirs</a>, view the directory stack
- <a href="builtins.html#end">end</a>, end a block of commands
- <a href="builtins.html#else">else</a>, conditionally execute a block of commands
- <a href="builtins.html#eval">eval</a>, evaluate a string as a command
- <a href="builtins.html#exec">exec</a>, replace the current process image with a new command
- <a href="builtins.html#exit">exit</a>, causes \c fish to quit
- <a href="builtins.html#fg">fg</a>, set a command to the foreground
- <a href="commands.html#fishd">fishd</a>, the universal variable daemon
- <a href="builtins.html#for">for</a>, perform a block of commands once for every element in a list
- <a href="builtins.html#function">function</a>, define a new function
- <a href="builtins.html#functions">functions</a>, print or erase functions
- <a href="commands.html#help">help</a>, show the fish documentation
- <a href="builtins.html#if">if</a>, conditionally execute a block of commands
- <a href="builtins.html#jobs">jobs</a>, print the currently running jobs
- <a href="commands.html#mimedb">mimedb</a>, view mimedata about a file
- <a href="commands.html#nextd">nextd</a>, move forward in the directory history
- <a href="builtins.html#not">not</a>, negates the exit status of any command
- <a href="commands.html#popd">popd</a>, move to the topmost directory on the directory stack
- <a href="commands.html#prevd">prevd</a>, move backwards in the direcotry stack
- <a href="commands.html#pushd">pushd</a>, push the surrent directory onto the directory stack
- <a href="builtins.html#random">random</a>, calculate a pseudo-random number
- <a href="builtins.html#return">return</a>, return from a function
- <a href="builtins.html#read">read</a>, read from a stream into an environment variable
- <a href="builtins.html#set">set</a>, set environment variables
- <a href="commands.html#set_color">set_color</a>, change the terminal colors
- <a href="builtins.html#switch">switch</a>, conditionally execute a block of commands
- <a href="commands.html#tokenize">tokenize</a>, split a string up into multiple tokens
- <a href="builtins.html#ulimit">ulimit</a>, set or get the shells resurce usage limits
- <a href="commandss.html#umask">umask</a>, set or get the file creation mask
- <a href="builtins.html#while">while</a>, perform a block of commands while a condition is met

For more information about these commands, use the <tt>--help</tt>
option of the command to display a longer explanation.

\section editor Command Line editor

The \c fish editor features copy and paste, a searchable history and
many editor functions that can be bound to special keyboard
shortcuts. The most important keybinding is probably the tab key, which is bound to the complete function. 
Here are some of the commands available in the editor:

- Tab completes the current token
- Home or Ctrl-a moves to the beginning of the line
- End or Ctrl-e moves to the end of line
- Left and right moves one character left or right
- Alt-left and Alt-right moves one word left or right, or moves forward/backward in the directory history if the commandline is empty
- Delete and backspace removes one character forwards or backwards
- Ctrl-c delete entire line
- Ctrl-d delete one character to the right of the cursor, unless the buffer is empty, in which case the shell will exit
- Ctrl-k move contents from cursor to end of line to <a href="#killring">killring</a>
- Ctrl-u move contents from beginning of line to cursor <a href="#killring">killring</a>
- Ctrl-l clear and repaint screen
- Ctrl-w move previous word to <a href="#killring">killring</a>
- Alt-d move next word to <a href="#killring">killring</a>
- Alt-w prints a short description of the command under the cursor 
- Alt-l lists the contents of the current directory, unless the cursor is over a directory argument, in which case the contents of that directory will be listed 
- Alt-k prints a list of all key bindings

You can change these key bindings by making an inputrc file. To do
this, copy the file /etc/fish_inputrc to your home directory and
rename it to '.fish_inputrc'. Now you can edit the file .fish_inputrc,
to change your key bindings. The fileformat of this file is described
in the manual page for readline. Use the command <tt>man readline</tt>
to read up on this syntax. Please note thet the list of key binding
functions in fish is different to that offered by readline. Currently,
the following functions are available:


- \c backward-char, moves one character to the left
- \c backward-delete-char, deletes one character of input to the left of the cursor
- \c backward-kill-line, move everything from the beginning of the line to the cursor to the killring
- \c backward-kill-word, move the word to the left of the cursor to the killring
- \c backward-word, move one word to the left
- \c beginning-of-history, move to the beginning of the history
- \c beginning-of-line, move to the beginning of the line
- \c complete, guess the remainder of the current token
- \c delete-char, delete one character to the right of the cursor
- \c delete-line, delete the entire line
- \c dump-functions, print a list of all key-bindings
- \c end-of-history, move to the end of the history
- \c end-of-line, move to the end of the line
- \c explain, print a description of possible problems with the current command
- \c forward-char, move one character to the right
- \c forward-word, move one word to the right
- \c history-search-backward, search the history for the previous match
- \c history-search-forward, search the history for the next match
- \c kill-line, move everything from the cursor to the end of the line to the killring
- \c kill-whole-line, move the line to the killring
- \c kill-word, move the next word to the killring
- \c yank, insert the latest entry of the killring into the buffer
- \c yank-pop, rotate to the previous entry of the killring



\subsection killring Copy and paste (Kill Ring) 

\c fish uses an Emacs style kill ring for copy and paste
functionality. Use Ctrl-K to cut from the current cursor position to
the end of the line. The string that is cut (a.k.a. killed) is
inserted into a linked list of kills, called the kill ring. To paste
the latest value from the kill ring use Ctrl-Y. After pasting, use
Meta-Y to rotate to the previous kill.

If the environment variable DISPLAY is set, \c fish will try to
connect to the X-windows server specified by this variable, and use
the clipboard on the X server for copying and pasting. 

\subsection history Searchable history

After a command has been entered, it is inserted at the end of a
history list. Any duplicate history items are automatically
removed. By pressing the up and down keys, the user can search
forwards and backwards in the history. If the current command line is
not empty when starting a history search, only the commands containing
the string entered into the command line are shown.

The history is stored in the file '.fish_history'. It is automatically
read on startup and merged on program exit.

Example:

To search for previous entries containing the word 'make', type 'make'
in the console and press the up key.

\section job-control Running multiple programs

Normally when \c fish starts a program, this program will be put in
the foreground, meaning it will take control of the terminal and \c
fish will be stopped until the program finishes. Sometimes this is not
desirable. For example, you may wish to start an application with a
graphical user interface from the terminal, and then be able to
continue using the shell. In such cases, there are several ways in
which the user can change <tt>fish</tt>'s behaviour.

-# By ending a command with the \& (ampersand) symbol, the user tells \c fish to put the specified command into the background. A background process will be run simultaneous with \c fish. \c fish will retain control of the terminal, so the program will not be able to read from the keyboard. 
-# By pressing ^Z, the user stops a currently running foreground  program and returns control to \c fish. Some programs do not support this feature, or remap it to another key. Gnu emacs uses ^X z to stop running.
-# By using the <a href="builtins.html#fg">fg</a> and <a href="builtins.html#bg">bg</a> builtin commands, the user can send any currently running job into the foreground or background.

\section initialization Initialization files

On startup, \c fish evaluates the file /etc/fish (Or ~/etc/fish if you
installed fish in your home directory) and ~/.fish, in that order. If
you want to run a command only on starting an interactive shell, use
the exit status of the command 'status --is-interactive' to determine
if the shell is interactive. If you want to run a command only on
starting a login shell, use 'status --is-login' instead.

Example:

If you want to add the directory ~/linux/bin to your PATH variable
when loging in, add the following to your ~/.fish file:

<pre>if status --is-login
	set PATH $PATH ~/linux/bin
end</pre>

If you want to run a set of commands when \c fish exits, use an <a
href='#event'>event handler</a> that is triggered by the exit of the
shell:

<pre>function on_exit --on-process %self
	echo fish is now exiting
end</pre>

<a href="#variables-universal">Universal variables</a> are stored in
the file .fishd.HOSTNAME, where HOSTNAME is the name of your
computer. Do not edit this file directly, edit them through fish
scripts or by using fish interactively instead.

\section other Other features

\subsection color Syntax highlighting

\c fish interprets the command line as it is typed and uses syntax
highlighting to provide feedback to the user. The most important
feedback is the detection of potential errors. By default, errors are
marked red.

Detected errors include:

- Non existing commands.
- Reading from or appending to a non existing file.
- Incorrect use of output redirects
- Mismatched parenthesis

When the cursor is over a parenthesis or a quote, \c fish also
highlights it's matching quote or parenthesis.

To customize the syntax highlighting, you can set the environment
variables \c fish_color_normal, \c fish_color_command, \c
fish_color_substitution, \c fish_color_redirection, \c fish_color_end,
\c fish_color_error, \c fish_color_param, \c fish_color_comment, \c
fish_color_match, \c fish_color_search_match, \c fish_color_cwd, \c
fish_pager_color_prefix, \c fish_pager_color_completion, \c
fish_pager_color_description and \c fish_pager_color_progress. Valid
values are \c black, \c red, \c green, \c brown, \c yellow, \c blue,
\c magenta, \c purple, \c cyan, \c white or \c normal. Setting one of
the above variables to normal will mean that the text color will be
set to the default foreground color for the terminal.

\subsection prompt Programmable prompt

By defining the \c fish_prompt function, the user can choose a custom
prompt. The \c fish_prompt function is executed and the output is used
as a prompt.

Example: 
<p>
The default \c fish prompt is 
</p>
<p>
<pre>
function fish_prompt -d "Write out the prompt"
	printf '\%s\@\%s\%s\\n\%s\%s\\n> ' (whoami) (hostname|cut -d . -f 1) (set_color \$fish_color_cwd) (prompt_pwd) (set_color normal)
end
</pre>
</p>

If you are using \c set_color or other commands that output escape
codes to change the font settings of the terminal, you must always and
every such sequence with a newline. This is needed since fish needs to
know that exact length of the prompt in order to tetect when the
cursor reaches the end of the line. Any newlines in the output of the
\c fish_prompt command are ignored.

\subsection title Programmable title

When running in a virtual terminal, the user define the \c fish_title
function to print a custom titlebar message. The \c fish_title
function is executed and the output is used as a titlebar message.

Example:
<p>
The default \c fish title is 
</p>
<p>
<pre>
function fish_title
	echo $_ ' '
	pwd
end
</pre>
</p>

\subsection event Event handlers

When defining a new function in fish, it is possible to make it into an
event handler, i.e. a function that is automatically run when a
specific event takes place. Events that can trigger a handler currently are:

* When a signal is delivered
* When a process or job exits
* When the value of a variable is updated

Example:

To specify a signal handler for the WINCH signal, write:

<pre>function --on-signal WINCH my_signal_handler
	echo Got WINCH signal!
end
</pre>

For more information on how to define new event handlers, see the
documentation for the <a href='builtins.html#function'>function</a>
command.

\section issues Common issues with fish

If you install fish in your home directory, fish will not work
correctly for any other user than yourself. This is because fish needs
it's initalization files to function properly. To solve this
problem, either copy the initialization files to each fish users home
directory, or install them in /etc.



\section todo Missing features and bugs

\subsection todo-features Missing features

- Complete vi-mode key bindings
- next-history-complete
- builtin wait command
- More completions (for example xterm, vim, 
konsole, gnome-terminal, dcop, cdrecord, cron, xargs
rlogin, telnet, rsync, arch, finger, nice, locate, 
bibtex, patch, aspell, xpdf,
zip, compress, wine, xmms, dig, wine, batch, cron, 
g++, javac, java, gcj, lpr, doxygen, whois, find)
- Undo support
- Check keybinding commands for output - if non has happened, don't repaint to reduce flicker
- The jobs builtin should be able to give information on a specific job, such as the pids of the processes in the job
- Syntax highlighting should mark cd to non-existing directories as an error


\subsection todo-possible Possible features

- Multiline editing
- tab completion could use smart casing
- Completions could support options beginning with a plus (like xterm
  +fbx) and options without dashes (like top p) Do we really want to
  complicate the code additionally for such a small number of programs?
- mouse support like zsh has with http://stchaz.free.fr/mouse.zsh 
  installed would be awesome
- suggest a completion on unique matches by writing it out in an understated color
- Maybe some functions should only be available from key-bindings. That way one could implement a large part of all the key-binding functions as regular fish functions without worrying about cluttering up the function name space.
- With a bit of tweakage, quite a few of the readline key-binding functions could be implemented in shellscript.
- Highlight beginning/end of block when moving over a block command
- Inclusion guards for the init files to make them evaluate only once, even if the user has installed fish both in /etc and in $HOME
- Do not actually load most of the shellscript functions on startup. Only load a tiny wrapper that will load the real function when needed. This should shave of CPU-time spent on parsing 500-1000 lines of code and ~50 kB of memory on startup, and is pretty easy to implement.
- Do not actually load/parse .fish_history, only mmap it and use some clever string handling. Should save ~150 kB of memory permanently, but is very hard to implement.
- command specific wildcarding (use case * instead of case '*', etc.)
- show the whole list of commands on using tab on an empty commandline
- Automatically move cursor to the end of the current token before completing
- Map variables. (export only the values. When expanding with no key specified, expand to all values.)

\subsection bugs Known bugs

- Completion for gcc -\#\#\# option doesn't work.
- Many completions are made specifically for the GNU 
version of a POSIX command
- Yanking weird characters from clipboard prints Unicode escapes

If you think you have found a bug not described here, please send a
report to <a href="mailto:axel@liljencrantz.se"> axel@liljencrantz.se
</a>.

\subsection Known issues

Older versions of Doxygen has bugs in the man-page generation which
cause the builtin help to render incorrectly. Version 1.2.14 is known
to have this problem.

In version 1.9.2, the installation prefix for fish rpms and debs
changed from /usr/local to /usr. Packages should automatically change
any instances of /usr/local/bin/fish in /etc/passwd to /usr/bin/fish,
but some programs, like screen, may need to be restarted to notice the
changes when upgrading from pre1.9.2 to 1.9.2 or later.  You may also
run into such problems when switching between using a package and
personal builds.

*/
/** \page design Design document

\section design-overview Design document

\subsection design-overview Overview

This is a description of the design principles that have been used to
design fish. The fish design has three high level goals. These are:

-# Everything that can be done in other shell languages should be
possible to do in fish, though fish may rely on external commands in
doing so. 
-# Fish should be user friendly, but not at the expense of expressiveness. 
Most tradeoffs between power and ease of use can be avoided with careful design.
-# Whenever possible without breaking the above goals, fish should
follow the Posix syntax.

To achive these high-level goals, the fish design relies on a number
of more specific design principles. These are presented below,
together with a rationale and a few examples for each.

\subsection ortho The law of orthogonality

The shell language should have a small set of orthogonal features. Any
situation where two features are related but not identical, one of them
should be removed, and the other should be made powerful and general
enough to handle all common use cases of either feature.

Rationale:

Related features make the language larger, which makes it harder to
learn. It also increases the size of the sourcecode, making the
program harder to maintain and update.

Examples:

- Here documents are too similar to using echo inside of a pipeline.
- Subshells, command substitution and process substitution are strongly related. \c fish only supports command substitution, the others can be achived either using a block or the psub shellscript function. 
- Having both aliases and functions is confusing, especially since both of them have limitations and problems. \c fish sunctions have none of the drawbacks of either syntax.
- The many Posix quoting styles are silly, especially \$''.


\subsection sep The law of minimalism

The shell should only contain features that cannot be implemented in
a reasonable way outside of the shell. A large performance decrease,
as well as some program complexity increase is acceptable in order to
improve separation.

Rationale:

A modular project is easier to maintain since smaller programs are far
easier to understand than larger ones. A modular project is also more
future proof since the modules can be individually
replaced. Modularity also decreases the severity of bugs, since there
is good hope that a bug, even a serious one, in one module, does not
take the whole system down.

Examples:

- Builtin commands should only be created when it cannot be
avoided. \c echo, \c kill, \c printf and \c time are among the commands 
that fish does not implement internally since they can be provided as 
external commands. Several other commands that are commonly implemented 
as builtins and can not be implemented as external commands,
including \c type, \c vared, \c pushd and \c popd are implemented as shellscript
functions in fish.
- Mathematical calculations, regex matching, generating lists of numbers
and many other funtions can easily be done in external programs. They 
should not be supported internally by the shell.

The law of minimalism does not imply that a large feature set is
bad. So long as a feature is not part of the shell itself, but a
separate command or at least a shellscript function, bloat is fine.

\subsection conf Configurability is the root of all evil

Every configuration option in a program is a place where the program
is too stupid to figure out for itself what the user really wants, and
should be considered a failiure of both the program and the programmer
who implemented it.

Rationale:

Different configuration options are a nightmare to maintain, since the
number of potential bugs caused by specific configuration combinations
quickly becomes an issue. Configuration options often imply
assumptions about the code which change when reimplementing the code,
causing issues with backwards compatibility. But mostly, configuration
options should be avoided since they simply should not exist, as the
program should be smart enough to do what is best, or at least a good
enough approximation of it.

Examples:

- Fish allows the user to set various syntax highlighting colors. This is needed because fish does not know what colors the terminal uses by default, which might make some things unreadable. The proper solution would be for text color preferences to be defined centrally by the user for all programs, and for the terminal emulator to send these color properties to fish.
- Fish does not allow you to set the history filename, the number of history entries, different language substyles or any number of other common shell configuration options.

A special note on the evils of configurability is the long list of
very useful features found in some shells, that are not turned on by
default. Both zsh and bash support command specific completions, but
no such completions are shipped with bash by default, and they are
turned of by default in zsh. Other features that zsh support that are
disabled by default include tab-completion of strings containing
wildcards, a sane completion pager and a history file.

\subsection user The law of user focus

When designing a program, one should first think about how to make a
intuitive and powerful program. Implementation issues should only be
considered once a user interface has been designed.

Rationale:

This design rule is different than the others, since it describes how
one should go about designing new features, not what the features
should be. The problem with focusing on what can be done, and what is
easy to do, is that to much of the implementation is exposed. This
means that the user must know a great deal about the underlying system
to be able to guess how the shell works, it also means that the
language will often be rather low-level.

Examples:

- There should only be one type of input to the shell, lists of commands. Loops, conditionals and variable assignments are all performed through regular commands.
- The differences between builtin commands, shellscript functions and builtin commands should be made as small as possible. Builtins and shellscript functions should have exactly the same types of argument expansion as other commands, should be possible to use in any position in a pipeline, and should support any io redirection.
- Instead of forking when performing command substitution to provide a fake variable scope, all fish commands are performed from the same process, and fish instead supports true scoping
- All blocks end with the \c end builtin

\subsection disc The law of discoverability

The shell should implement it's features in a way that makes them as
easy as possible for the user to discover for her/himself.

Rationale:

A program whose features are discoverable makes a new user into an
expert in a shorter span of time, since the user will learn how to use
the program simply by using it. 

The main benefit of a graphical program over a command line-based
program is discoverability. In a graphical program, one can discover
all the common features by simply looking at the user interface and
guessing what the different buttons, menus and other widgets do. The
traditional way to discover features in commandline programs is
through manual pages. This requires both that the user starts to use a
different program, and the she/he then remembers the new information
until the next time she/he uses the same program.

Examples:

- Everything should be tab-completable, and every tab completion should have a description
- Every syntax error and error in a builtin command should contain an error message describing what went wrong and a relevant help page. Whenever possible, errors should be flagged red by the syntax highlighter.
- The help manual should be easy to read, easily available from the shell, complete and contain many examples
- The language should be uniform, so that once the user understands the command/argument syntax, he will know the whole language, and be able to use tab-completion to discover new featues.

*/
/** \page about About fish


\section about-program About the program

\c fish is meant to be used for interactive shell tasks on a modern
UNIX-like workstation. It is much more important for me to keep the
code maintainable, readable and bug free than to support esoteric old
hardware, software or wetware. As such, the program is often wildly
inefficient in its use of memory and CPU cycles. On my system, \c fish
uses a little less than half a megabyte of memory, a number that could
be significantly reduced with a little effort. \c fish performs a lot
of linear searches of things that could be done in logarithmic time,
does not usually cache file system data or other search result, and
uses the fork() call promiscuosly. None of these things matter because
\c fish is still fast enough to be perceived as instantaneous on a
semi-modern computer thanks to the miracles of copy-on-write, OS-level
caching and Moores law, and it only uses a fraction of the memory used
by most terminal emulators to display it. If this program was anything
other than an amusing hobby for me, I would of course feel otherwise,
but since my time is limited, this is the way it must be.


\section about-code About the source code

Fish is written using the ellemtel indentation style, using four space
tabs. \c fish regularly performs a large set of sanity checks to make
sure it is in a sane state. If not, the program will terminate before
it can do any harm.

Do not edit the file builtin_help.c, it is automatically generated.


\section about-documentation About the documentation

The documentation for \c fish is written for Doxygen. All header files
are pretty heavily commented. 

Since it was desirable to use the same text files for producing the
HTML documentation as for producing the internal help output, some
rather ugly kludges had to be used for writing the documentation for
the builtin commands.

The directory doc_src contains a file called doc.hdr, containing
various general documentation for \c fish, and a large number of .txt
files. Each txt file contains the documentation for one \c fish
builtin. When creating the main doxygen documentation, all these files
are concatenated into one file, called doc.h. When creating the
internal documentation, each of the .txt files is converted to a .h
file by supplying a doxygen header/footer. These headers are then
converted into man style manuals, which in turn are converted to C
code by a script called gen_hdr.sh. The resulting C-file,
builtin_help.c, can then by linked into \c fish. This method is probably
not the most robust, elegant or clever method for generating
documentation. If someone has a suggestion of how to do i better,
please notify me.
*/
/** \page difference Why fish?
\section difference-overview What is different about fish?

This page is a summary of differences between \c fish and other shells. 

\subsection difference-completion Tab completion features

\c fish, like many other shells, performs tab completion, i.e. the shell
tries to guess what the user is typing and complete the users
sentences whenever the user presses the tab key. If the shell finds
more than one possible completion, a list of all completions is
displayed when the users double taps on tab. \c fish extends tab
completion functionality in several ways:

- \c fish performs file completion on strings containing wildcards
- When showing a list of possible completions, \c fish adds a 
description to each completion. For files this description is a 
description of the format or filetype, like 'C source code', 
'Character device' or 'Executable'. For variables, if the 
value is short enough, the variable value will be displayed. For 
commands, if there is room and few enough commands, the whatis 
description of the command is used. 
- \c fish has extensive command specific completions, including 
completion of specific options. This is very powerful in combination 
with completion descriptions, as the user can see what each option does 
without consulting the manual. Simply type the command you wish to use, 
type a dash and double tab TAB, and the screen will fill with a list of 
the commands options and a description of what they do. 
- \c fish uses a decent pager when the results won't fit on one 
screen. The pager can scroll up and down, both one row and one page at
a time, and if any non movement key is pressed the pager exits without
consuming the character.  Therefore, there is no need to press 
'q' to exit before typing your completion.

Some examples of the completions performed by \c fish

- When completing an argument for the man command, the whatis 
database is searched for manual pages as completions.
- When completing a command name, the whatis database is searched 
for each possible command, and the description returned is used 
as the description of the command.
- When completing an argument for the make command, the Makefile 
in the current directory is searched for targets.

\subsection difference-killring X-Windows Copy and paste

\c fish supports using the X-Windows clipboard for storing copy and
paste information. This feature is automatically enabled if the
DISPLAY environment variable is set. For more information on how to
use copy and paste in \c fish, read <a href="index.html#killring">
this section</a>. This means you can easily share commands and strings
between different shell sessions and applications.

\subsection difference-open Simple launching of default applications

The open command uses the mimetype database (Also used by both Gnome
or KDE) to launch the default application for a file. Just type
<tt>open *.html</tt> and all the HTML files in your current directory
will be opened in your default browser. No longer will you have to
convert your filenames to URLS, remember clunky Open Office command
names, worry about absolute paths or any the other common pitfalls when
opening files from the commandline.

\subsection difference-help Help

\c fish is heavily commented. Both the source code and the
program in general features a great deal of easily accessible
documentation. The <tt>help</tt> command is used to display HTML-based
help files. Just type <tt>help</tt> and a subject, and the help system
will try to fill your needs. To view the page you are reading right
now, you could simply type <tt>help difference</tt>. <tt>help</tt>
also works great together with tab completion. Write \c help and
double tap on tab, a list of all help sections will be displayed, with
a description of the content of each section.

Also, all builtin commands have a help option. Passing '-h' or
'--help' to any builtin will give you the same help as the help
command, but formated for output on screen.

\subsection difference-highlighting Syntax highlighting

\c fish performs syntax highlighting of commands as they're
entered. Pretty colors may look nice (or awful, depending on your
taste), but the real advantage is error flagging. The syntax
highlighting function does extensive error cheching and will flag many
common errors such as misspelling a command or option, or reading from a
non-existent file.

\c fish also highlights matching quotes and parenthesis as the cursor
moves over them. This is very useful when typing long, complex
commands.

\subsection difference-terminal Terminal handling

\c fish knows it's terminal. \c fish uses the terminfo database
to get more information on the current terminal. Some of the terminal
handling features of \c fish are:

- Backspace and delete work more often in \c fish thanks to the use of 
terminfo. If you've been bitten by this, you'll know what this means.
- If the screen has been written to when \c fish was in the foreground, 
this is detected and the command line is redrawn. 
- Process notifications, like jobs ending or being stopped by signals,
are printed to the screen at once, not whenever the user presses the enter key.

\c fish uses wide character strings internally, including double width
characters, so it should be ready for all your Unicode needs.

\subsection difference-history Smart history

\c fish features an intelligent history that automatically removes any
duplicate items. Searching is performed by entering a search string
and using the up/down arrow keys to go to the next/previous match. On
exit, \c fish performs a merge between the history on file and the
history in memory history, thus making sure that multiple copies of \c
fish running concurrently will not erase each others history
information.

\subsection difference-simple Simplicity

\c fish has a simple syntax. There is only one form of
alias/function/whatever, accessed through the <tt>function</tt>
builtin. The are very few builtins, \c fish relies on normal commands
like <tt>echo</tt>, <tt>kill</tt>, <tt>printf</tt> and <tt>time</tt>
instead of reimplementing them as builtins.

Token separation is performed before variable expansion. This means
that even if a variable contains spaces, it will never be separated
into multiple arguments. If you want to tokenize a string, you can use
the <a href="commands.html#tokenize">tokenize</a> command.

Command substitution is specified using parenthesis, as in <tt>set name (whoami)</tt>. 

There is no math mode, use bc.

The POSIX way of setting variables is <i>lame</i>. Whitespace
sensitive languages are awful. "foo=bar" and "foo = bar" should not
mean different things. \c fish uses a builtin, <tt>set</tt> to set and
remove environment variables. While this may seem a bit obscure, this
makes for a very consistent language. In fish, everything, including
the loops, assignments and switch/case statements is a command.

In \c fish, all block types end with the \c end command.

*/
/** \page license License

\c fish Copyright (C) 2005 Axel Liljencrantz. It is released under the
GNU General Public License. The license agreement is included
below. For more information on the GNU project and its goals, visit <a
href="http://www.gnu.org">the GNU homepage</a>.

\c fish also contains small amounts of code under the BSD
license, namely versions of the two functions strlcat and strlcpy,
modified for use with wide character strings. This code is copyrighted
by Todd C. Miller.

The XSel command, written and copyrighted by Conrad Parker, is
distributed together with \c fish. It is released under the MIT license.

The xdgmime library, written and copyrighted by Red Hat, Inc, is used
by the mimedb command, which is a part of fish. It is released under
the LGPL license.

<H2><A NAME="SEC1" HREF="gpl.html#TOC1">GNU GENERAL PUBLIC LICENSE</A></H2>
<P>
Version 2, June 1991

</P>

<PRE>
Copyright (C) 1989, 1991 Free Software Foundation, Inc.  
59 Temple Place - Suite 330, Boston, MA  02111-1307, USA

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
</PRE>


<H2><A NAME="SEC2" HREF="gpl.html#TOC2">Preamble</A></H2>

<P>
The licenses for most software are designed to take away your
freedom to share and change it.  By contrast, the GNU General Public
License is intended to guarantee your freedom to share and change free
software--to make sure the software is free for all its users.  This
General Public License applies to most of the Free Software
Foundation's software and to any other program whose authors commit to
using it.  (Some other Free Software Foundation software is covered by
the GNU Library General Public License instead.)  You can apply it to
your programs, too.

</P>
<P>
When we speak of free software, we are referring to freedom, not
price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
this service if you wish), that you receive source code or can get it
if you want it, that you can change the software or use pieces of it
in new free programs; and that you know you can do these things.

</P>
<P>
To protect your rights, we need to make restrictions that forbid
anyone to deny you these rights or to ask you to surrender the rights.
These restrictions translate to certain responsibilities for you if you
distribute copies of the software, or if you modify it.

</P>
<P>

For example, if you distribute copies of such a program, whether
gratis or for a fee, you must give the recipients all the rights that
you have.  You must make sure that they, too, receive or can get the
source code.  And you must show them these terms so they know their
rights.

</P>
<P>
We protect your rights with two steps: (1) copyright the software, and
(2) offer you this license which gives you legal permission to copy,
distribute and/or modify the software.

</P>
<P>
Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
software.  If the software is modified by someone else and passed on, we
want its recipients to know that what they have is not the original, so
that any problems introduced by others will not reflect on the original
authors' reputations.

</P>
<P>
Finally, any free program is threatened constantly by software
patents.  We wish to avoid the danger that redistributors of a free
program will individually obtain patent licenses, in effect making the
program proprietary.  To prevent this, we have made it clear that any
patent must be licensed for everyone's free use or not licensed at all.

</P>
<P>
The precise terms and conditions for copying, distribution and
modification follow.


</P>


<H2><A NAME="SEC3" HREF="gpl.html#TOC3">TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION</A></H2>


<P>

<STRONG>0.</STRONG>
This License applies to any program or other work which contains
a notice placed by the copyright holder saying it may be distributed
under the terms of this General Public License.  The "Program", below,
refers to any such program or work, and a "work based on the Program"
means either the Program or any derivative work under copyright law:
that is to say, a work containing the Program or a portion of it,
either verbatim or with modifications and/or translated into another
language.  (Hereinafter, translation is included without limitation in
the term "modification".)  Each licensee is addressed as "you".
<P>

Activities other than copying, distribution and modification are not
covered by this License; they are outside its scope.  The act of
running the Program is not restricted, and the output from the Program
is covered only if its contents constitute a work based on the
Program (independent of having been made by running the Program).
Whether that is true depends on what the Program does.

<P>

<STRONG>1.</STRONG>
You may copy and distribute verbatim copies of the Program's
source code as you receive it, in any medium, provided that you
conspicuously and appropriately publish on each copy an appropriate
copyright notice and disclaimer of warranty; keep intact all the
notices that refer to this License and to the absence of any warranty;
and give any other recipients of the Program a copy of this License
along with the Program.
<P>

You may charge a fee for the physical act of transferring a copy, and
you may at your option offer warranty protection in exchange for a fee.
<P>

<STRONG>2.</STRONG>
You may modify your copy or copies of the Program or any portion
of it, thus forming a work based on the Program, and copy and
distribute such modifications or work under the terms of Section 1
above, provided that you also meet all of these conditions:
<P>

<DL>

<DT>
<DD>
<STRONG>a)</STRONG>
You must cause the modified files to carry prominent notices
stating that you changed the files and the date of any change.
</DD>
</DT>
</DL>
<P>
<DL>
<DT>
<DD>
<STRONG>b)</STRONG>
You must cause any work that you distribute or publish, that in
whole or in part contains or is derived from the Program or any
part thereof, to be licensed as a whole at no charge to all third
parties under the terms of this License.

</DD>
</DT>
</DL>
<P>
<DL>
<DT>
<DD>
<STRONG>c)</STRONG>
If the modified program normally reads commands interactively
when run, you must cause it, when started running for such
interactive use in the most ordinary way, to print or display an
announcement including an appropriate copyright notice and a
notice that there is no warranty (or else, saying that you provide
a warranty) and that users may redistribute the program under
these conditions, and telling the user how to view a copy of this
License.  (Exception: if the Program itself is interactive but
does not normally print such an announcement, your work based on
the Program is not required to print an announcement.)
</DD>
</DT>
</DL>
<P>

These requirements apply to the modified work as a whole.  If
identifiable sections of that work are not derived from the Program,
and can be reasonably considered independent and separate works in
themselves, then this License, and its terms, do not apply to those
sections when you distribute them as separate works.  But when you
distribute the same sections as part of a whole which is a work based
on the Program, the distribution of the whole must be on the terms of
this License, whose permissions for other licensees extend to the
entire whole, and thus to each and every part regardless of who wrote it.

<P>

Thus, it is not the intent of this section to claim rights or contest
your rights to work written entirely by you; rather, the intent is to
exercise the right to control the distribution of derivative or
collective works based on the Program.
<P>

In addition, mere aggregation of another work not based on the Program
with the Program (or with a work based on the Program) on a volume of
a storage or distribution medium does not bring the other work under
the scope of this License.

<P>

<STRONG>3.</STRONG>
You may copy and distribute the Program (or a work based on it,
under Section 2) in object code or executable form under the terms of
Sections 1 and 2 above provided that you also do one of the following:


<!-- we use this doubled UL to get the sub-sections indented, -->
<!-- while making the bullets as unobvious as possible. -->

<DL>
<DT>

<DD>
<STRONG>a)</STRONG>
Accompany it with the complete corresponding machine-readable
source code, which must be distributed under the terms of Sections
1 and 2 above on a medium customarily used for software interchange; or,
</DD>
</DT>
</DL>
<P>
<DL>
<DT>
<DD>
<STRONG>b)</STRONG>
Accompany it with a written offer, valid for at least three
years, to give any third party, for a charge no more than your
cost of physically performing source distribution, a complete
machine-readable copy of the corresponding source code, to be
distributed under the terms of Sections 1 and 2 above on a medium
customarily used for software interchange; or,
</DD>

</DT>
</DL>
<P>
<DL>
<DT>
<DD>
<STRONG>c)</STRONG>
Accompany it with the information you received as to the offer
to distribute corresponding source code.  (This alternative is
allowed only for noncommercial distribution and only if you
received the program in object code or executable form with such
an offer, in accord with Subsection b above.)
</DD>
</DT>
</DL>
<P>

The source code for a work means the preferred form of the work for
making modifications to it.  For an executable work, complete source
code means all the source code for all modules it contains, plus any
associated interface definition files, plus the scripts used to
control compilation and installation of the executable.  However, as a
special exception, the source code distributed need not include
anything that is normally distributed (in either source or binary
form) with the major components (compiler, kernel, and so on) of the
operating system on which the executable runs, unless that component
itself accompanies the executable.
<P>

If distribution of executable or object code is made by offering
access to copy from a designated place, then offering equivalent
access to copy the source code from the same place counts as
distribution of the source code, even though third parties are not
compelled to copy the source along with the object code.
<P>

<STRONG>4.</STRONG>
You may not copy, modify, sublicense, or distribute the Program
except as expressly provided under this License.  Any attempt
otherwise to copy, modify, sublicense or distribute the Program is
void, and will automatically terminate your rights under this License.
However, parties who have received copies, or rights, from you under
this License will not have their licenses terminated so long as such
parties remain in full compliance.

<P>

<STRONG>5.</STRONG>
You are not required to accept this License, since you have not
signed it.  However, nothing else grants you permission to modify or
distribute the Program or its derivative works.  These actions are
prohibited by law if you do not accept this License.  Therefore, by
modifying or distributing the Program (or any work based on the
Program), you indicate your acceptance of this License to do so, and
all its terms and conditions for copying, distributing or modifying
the Program or works based on it.

<P>

<STRONG>6.</STRONG>

Each time you redistribute the Program (or any work based on the
Program), the recipient automatically receives a license from the
original licensor to copy, distribute or modify the Program subject to
these terms and conditions.  You may not impose any further
restrictions on the recipients' exercise of the rights granted herein.
You are not responsible for enforcing compliance by third parties to
this License.

<P>

<STRONG>7.</STRONG>
If, as a consequence of a court judgment or allegation of patent
infringement or for any other reason (not limited to patent issues),
conditions are imposed on you (whether by court order, agreement or
otherwise) that contradict the conditions of this License, they do not
excuse you from the conditions of this License.  If you cannot
distribute so as to satisfy simultaneously your obligations under this
License and any other pertinent obligations, then as a consequence you
may not distribute the Program at all.  For example, if a patent
license would not permit royalty-free redistribution of the Program by
all those who receive copies directly or indirectly through you, then
the only way you could satisfy both it and this License would be to
refrain entirely from distribution of the Program.
<P>

If any portion of this section is held invalid or unenforceable under
any particular circumstance, the balance of the section is intended to
apply and the section as a whole is intended to apply in other
circumstances.
<P>

It is not the purpose of this section to induce you to infringe any
patents or other property right claims or to contest validity of any
such claims; this section has the sole purpose of protecting the
integrity of the free software distribution system, which is
implemented by public license practices.  Many people have made
generous contributions to the wide range of software distributed
through that system in reliance on consistent application of that
system; it is up to the author/donor to decide if he or she is willing
to distribute software through any other system and a licensee cannot
impose that choice.
<P>

This section is intended to make thoroughly clear what is believed to
be a consequence of the rest of this License.


<P>

<STRONG>8.</STRONG>
If the distribution and/or use of the Program is restricted in
certain countries either by patents or by copyrighted interfaces, the
original copyright holder who places the Program under this License
may add an explicit geographical distribution limitation excluding
those countries, so that distribution is permitted only in or among
countries not thus excluded.  In such case, this License incorporates
the limitation as if written in the body of this License.

<P>

<STRONG>9.</STRONG>
The Free Software Foundation may publish revised and/or new versions
of the General Public License from time to time.  Such new versions will
be similar in spirit to the present version, but may differ in detail to
address new problems or concerns.
<P>

Each version is given a distinguishing version number.  If the Program
specifies a version number of this License which applies to it and "any
later version", you have the option of following the terms and conditions
either of that version or of any later version published by the Free
Software Foundation.  If the Program does not specify a version number of
this License, you may choose any version ever published by the Free Software
Foundation.

<P>

<STRONG>10.</STRONG>
If you wish to incorporate parts of the Program into other free
programs whose distribution conditions are different, write to the author
to ask for permission.  For software which is copyrighted by the Free
Software Foundation, write to the Free Software Foundation; we sometimes
make exceptions for this.  Our decision will be guided by the two goals
of preserving the free status of all derivatives of our free software and
of promoting the sharing and reuse of software generally.



<P><STRONG>NO WARRANTY</STRONG></P>

<P>

<STRONG>11.</STRONG>
BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS
TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
REPAIR OR CORRECTION.

<P>

<STRONG>12.</STRONG>

IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.

<P>


<H2>END OF TERMS AND CONDITIONS</H2>



<H2><A NAME="SEC4" HREF="gpl.html#TOC4">How to Apply These Terms to Your New Programs</A></H2>

<P>
If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these terms.

</P>

<P>
To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.

</P>

<PRE>
<VAR>one line to give the program's name and an idea of what it does.</VAR>
Copyright (C) <VAR>yyyy</VAR>  <VAR>name of author</VAR>

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
</PRE>

<P>
Also add information on how to contact you by electronic and paper mail.

</P>
<P>
If the program is interactive, make it output a short notice like this
when it starts in an interactive mode:

</P>

<PRE>
Gnomovision version 69, Copyright (C) <VAR>year</VAR> <VAR>name of author</VAR>
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
type `show w'.  This is free software, and you are welcome
to redistribute it under certain conditions; type `show c' 
for details.
</PRE>

<P>

The hypothetical commands <TT>`show w'</TT> and <TT>`show c'</TT> should show
the appropriate parts of the General Public License.  Of course, the
commands you use may be called something other than <TT>`show w'</TT> and
<TT>`show c'</tt>; they could even be mouse-clicks or menu items--whatever
suits your program.

</P>
<P>
You should also get your employer (if you work as a programmer) or your
school, if any, to sign a "copyright disclaimer" for the program, if
necessary.  Here is a sample; alter the names:

</P>

<PRE>
Yoyodyne, Inc., hereby disclaims all copyright
interest in the program `Gnomovision'
(which makes passes at compilers) written 
by James Hacker.

<VAR>signature of Ty Coon</VAR>, 1 April 1989
Ty Coon, President of Vice
</PRE>

<P>
This General Public License does not permit incorporating your program into
proprietary programs.  If your program is a subroutine library, you may
consider it more useful to permit linking proprietary applications with the
library.  If this is what you want to do, use the 
<a href="/licenses/lgpl.html">GNU Lesser General Public License</a>
instead of this License.

<p>

<HR>

<h2>License for wcslcat and wcslcpy</h2>

\c fish also contains small amounts of code under the BSD
license, namely versions of the two functions strlcat and strlcpy,
modified for use with wide character strings. This code is copyrighted
by Todd C. Miller.

Permission to use, copy, modify, and distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
PERFORMANCE OF THIS SOFTWARE.

<h2>License for XSel</h2>

The XSel command, written and copyrighted by Conrad Parker, is
distributed together with \c fish. 


It is Copyright (C) 2001 Conrad Parker <conrad@vergenet.net>

Permission to use, copy, modify, distribute, and sell this software
and its documentation for any purpose is hereby granted without fee,
provided that the above copyright notice appear in all copies and that
both that copyright notice and this permission notice appear in
supporting documentation. No representations are made about the
suitability of this software for any purpose. It is provided "as is"
without express or implied warranty.

*/