fish-shell/doc_src/cmds/set.rst

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.. _cmd-set:
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set - display and change shell variables
========================================
Synopsis
--------
docs synopsis: add HTML highlighing and automate manpage markup Recent synopsis changes move from literal code blocks to [RST line blocks]. This does not translate well to HTML: it's not rendered in monospace, so aligment is lost. Additionally, we don't get syntax highlighting in HTML, which adds differences to our code samples which are highlighted. We hard-wrap synopsis lines (like code blocks). To align continuation lines in manpages we need [backslashes in weird places]. Combined with the **, *, and `` markup, it's a bit hard to get the alignment right. Fix these by moving synopsis sources back to code blocks and compute HTML syntax highlighting and manpage markup with a custom Sphinx extension. The new Pygments lexer can tokenize a synopsis and assign the various highlighting roles, which closely matches fish's syntax highlighing: - command/keyword (dark blue) - parameter (light blue) - operator like and/or/not/&&/|| (cyan) - grammar metacharacter (black) For manpage output, we don't project the fish syntax highlighting but follow the markup convention in GNU's man(1): bold text type exactly as shown. italic text replace with appropriate argument. To make it easy to separate these two automatically, formalize that (italic) placeholders must be uppercase; while all lowercase text is interpreted literally (so rendered bold). This makes manpages more consistent, see string-join(1) and and(1). Implementation notes: Since we want manpage formatting but Sphinx's Pygments highlighing plugin does not support manpage output, add our custom "synopsis" directive. This directive parses differently when manpage output is specified. This means that the HTML and manpage build processes must not share a cache, because the parsed doctrees are cached. Work around this by using separate cache locations for build targets "sphinx-docs" (which creates HTML) and "sphinx-manpages". A better solution would be to only override Sphinx's ManualPageBuilder but that would take a bit more code (ideally we could override ManualPageWriter but Sphinx 4.3.2 doesn't really support that). --- Alternative solution: stick with line blocks but use roles like :command: or :option: (or custom ones). While this would make it possible to produce HTML that is consistent with code blocks (by adding a bit of CSS), the source would look uglier and is harder to maintain. (Let's say we want to add custom formatting to the [|] metacharacters in HTML. This is much easier with the proposed patch.) --- [RST line blocks]: https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#line-blocks [backslashes in weird places]: https://github.com/fish-shell/fish-shell/pull/8626#discussion_r782837750
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.. synopsis::
set
set (-f | --function) (-l | local) (-g | --global) (-U | --universal)
set [-Uflg] NAME [VALUE ...]
set [-Uflg] NAME[[INDEX ...]] [VALUE ...]
set (-a | --append) [-flgU] NAME VALUE ...
set (-q | --query) (-e | --erase) [-flgU] [NAME][[INDEX]] ...]
set (-S | --show) [NAME ...]
Description
-----------
``set`` manipulates :ref:`shell variables <variables>`.
If both *NAME* and *VALUE* are provided, ``set`` assigns any values to variable *NAME*.
Variables in fish are :ref:`lists <variables-lists>`, multiple values are allowed.
One or more variable *INDEX* can be specified including ranges (not for all options.)
If no *VALUE* is given, the variable will be set to the empty list i.e. ``''``.
If ``set`` is ran without arguments, it prints the names and values of all shell variables in sorted order.
Passing :ref:`scope <variables-scope>` or :ref:`export <variables-export>` flags allows filtering this to only matching variables, so ``set --local`` would only show local variables.
With ``--erase`` and optionally a scope flag ``set`` will erase the matching variable (or the variable of that name in the smallest possible scope).
With ``--show``, ``set`` will describe the given variable names, explaining how they have been defined - in which scope with which values and options.
The following scope control variable scope:
**-U** or **--universal**
Sets a universal variable.
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The variable will be immediately available to all the user's ``fish`` instances on the machine, and will be persist across restarts of the shell.
**-f** or **--function**
Sets a variable scoped to the executing function.
It is erased when the function ends.
**-l** or **--local**
Sets a locally-scoped variable in this block.
It is erased when the block ends.
Outside of a block, this is the same as **--function**.
Add `set --function` (#8145) * Add `set --function` This makes the function's scope available, even inside of blocks. Outside of blocks it's the toplevel local scope. This removes the need to declare variables locally before use, and will probably end up being the main way variables get set. E.g.: ```fish set -l thing if condition set thing one else set thing two end ``` could be written as ```fish if condition set -f thing one else set -f thing two end ``` Note: Many scripts shipped with fish use workarounds like `and`/`or` instead of `if`, so it isn't easy to find good examples. Also, if there isn't an else-branch in that above, just with ```fish if condition set -f thing one end ``` that means something different from setting it before! Now, if `condition` isn't true, it would use a global (or universal) variable of te same name! Some more interesting parts: Because it *is* a local scope, setting a variable `-f` and `-l` in the toplevel of a function ends up the same: ```fish function foo2 set -l foo bar set -f foo baz # modifies the *same* variable! end ``` but setting it locally inside a block creates a new local variable that shadows the function-scoped variable: ```fish function foo3 set -f foo bar begin set -l foo banana # $foo is banana end # $foo is bar again end ``` This is how local variables already work. "Local" is actually "block-scoped". Also `set --show` will only show the closest local scope, so it won't show a shadowed function-level variable. Again, this is how local variables already work, and could be done as a separate change. As a fun tidbit, functions with --no-scope-shadowing can now use this to set variables in the calling function. That's probably okay given that it's already an escape hatch (but to be clear: if it turns out to problematic I reserve the right to remove it). Fixes #565
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**-g** or **--global**
Sets a globally-scoped variable.
Global variables are available to all functions running in the same shell.
They can be modified or erased.
These options modify how variables operate:
**--export** or **-x**
Causes the specified shell variable to be exported to child processes (making it an "environment variable").
**--unexport** or **-u**
Causes the specified shell variable to NOT be exported to child processes.
**--path**
Treat specified variable as a :ref:`path variable <variables-path>`; variable will be split on colons (``:``) and will be displayed joined by colons colons when quoted (``echo "$PATH"``) or exported.
**--unpath**
Causes variable to no longer be tred as a :ref:`path variable <variables-path>`.
Note: variables ending in "PATH" are automatically path variables.
Further options:
**-a** or **--append** *NAME* *VALUE* ...
Appends *VALUES* to the current set of values for variable **NAME**.
Can be used with **--prepend** to both append and prepend at the same time.
This cannot be used when assigning to a variable slice.
**-p** or **--prepend** *NAME* *VALUE* ...
Prepends *VALUES* to the current set of values for variable **NAME**.
This can be used with **--append** to both append and prepend at the same time.
This cannot be used when assigning to a variable slice.
**-e** or **--erase** *NAME*[*INDEX*]
Causes the specified shell variables to be erased.
Supports erasing from multiple scopes at once.
Individual items in a variable at *INDEX* in brackets can be specified.
**-q** or **--query** *NAME*[*INDEX*]
Test if the specified variable names are defined.
If an *INDEX* is provided, check for items at that slot.
Does not output anything, but the shell status is set to the number of variables specified that were not defined, up to a maximum of 255.
If no variable was given, it also returns 255.
**-n** or **--names**
List only the names of all defined variables, not their value.
The names are guaranteed to be sorted.
**-S** or **--show**
Shows information about the given variables.
If no variable names are given then all variables are shown in sorted order.
It shows the scopes the given variables are set in, along with the values in each and whether or not it is exported.
No other flags can be used with this option.
**-L** or **--long**
Do not abbreviate long values when printing set variables.
**-h** or **--help**
Displays help about using this command.
If a variable is set to more than one value, the variable will be a list with the specified elements.
If a variable is set to zero elements, it will become a list with zero elements.
If the variable name is one or more list elements, such as ``PATH[1 3 7]``, only those list elements specified will be changed.
If you specify a negative index when expanding or assigning to a list variable, the index will be calculated from the end of the list.
For example, the index -1 means the last index of a list.
The scoping rules when creating or updating a variable are:
- Variables may be explicitly set as universal, global, function, or local.
Variables with the same name but in a different scope will not be changed.
- If the scope of a variable is not explicitly set *but a variable by that name has been previously defined*, the scope of the existing variable is used.
If the variable is already defined in multiple scopes, the variable with the narrowest scope will be updated.
- If a variable's scope is not explicitly set and there is no existing variable by that name, the variable will be local to the currently executing function.
Note that this is different from using the ``-l`` or ``--local`` flag, in which case the variable will be local to the most-inner currently executing block, while without them the variable will be local to the function as a whole.
If no function is executing, the variable will be set in the global scope.
The exporting rules when creating or updating a variable are identical to the scoping rules for variables:
- Variables may be explicitly set to either exported or not exported.
When an exported variable goes out of scope, it is unexported.
- 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 exported or unexported and has never before been defined, the variable will not be exported.
In query mode, the scope to be examined can be specified.
Whether the variable has to be a path variable or exported can also be specified.
In erase mode, if variable indices are specified, only the specified slices of the list variable will be erased.
``set`` requires all options to come before any other arguments.
For example, ``set flags -l`` will have the effect of setting the value of the variable :envvar:`flags` to '-l', not making the variable local.
Exit status
-----------
In assignment mode, ``set`` does not modify the exit status, but passes along whatever :envvar:`status` was set, including by command substitutions.
This allows capturing the output and exit status of a subcommand, like in ``if set output (command)``.
In query mode, the exit status is the number of variables that were not found.
In erase mode, ``set`` exits with a zero exit status in case of success, with a non-zero exit status if the commandline was invalid, if any of the variables did not exist or was a :ref:`special read-only variable <variables-special>`.
Examples
--------
Print all global, exported variables::
> set -gx
Set the value of the variable _$foo_ to be 'hi'.::
> set foo hi
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Append the value "there" to the variable $foo::
> set -a foo there
Remove _$smurf_ from the scope::
> set -e smurf
Remove _$smurf_ from the global and universal scoeps::
> set -e -Ug smurf
Change the fourth element of the $PATH list to ~/bin::
> set PATH[4] ~/bin
Outputs the path to Python if ``type -p`` returns true::
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if set python_path (type -p python)
echo "Python is at $python_path"
end
Setting a variable doesn't modify $status; a command substitution still will, though::
> echo $status
0
> false
> set foo bar
> echo $status
1
> true
> set foo banana (false)
> echo $status
1
``VAR=VALUE command`` sets a variable for just one command, like other shells.
This runs fish with a temporary home directory::
> HOME=(mktemp -d) fish
(which is essentially the same as)::
> begin; set -lx HOME (mktemp -d); fish; end
Notes
-----
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- Fish versions prior to 3.0 supported the syntax ``set PATH[1] PATH[4] /bin /sbin``, which worked like ``set PATH[1 4] /bin /sbin``.