fish-shell/doc_src/cmds/switch.rst

.. _cmd-switch:

switch - conditionally execute a block of commands
==================================================

Synopsis
--------

.. synopsis::

    switch VALUE; [case [GLOB ...]; [COMMANDS ...]; ...] end

Description
-----------

``switch`` performs one of several blocks of commands, depending on whether a specified value equals one of several globbed values. ``case`` is used together with the ``switch`` statement in order to determine which block should be executed.

Each ``case`` command is given one or more parameters. The first ``case`` command with a parameter that matches the string specified in the switch command will be evaluated. ``case`` parameters may contain globs. These need to be escaped or quoted in order to avoid regular glob expansion using filenames.

Note that fish does not fall through on case statements. Only the first matching case is executed.

Note that :doc:`break <break>` cannot be used to exit a case/switch block early like in other languages. It can only be used in loops.

Note that command substitutions in a case statement will be evaluated even if its body is not taken. All substitutions, including command substitutions, must be performed before the value can be compared against the parameter.


Example
-------

If the variable ``$animal`` contains the name of an animal, the following code would attempt to classify it:

::

    switch $animal
        case cat
            echo evil
        case wolf dog human moose dolphin whale
            echo mammal
        case duck goose albatross
            echo bird
        case shark trout stingray
            echo fish
        case '*'
            echo I have no idea what a $animal is
    end


If the above code was run with ``$animal`` set to ``whale``, the output
would be ``mammal``.
docs: Add labels to all commands This allows us to use :ref: references, which don't require hardcoding it as html [ci skip] 2019-03-31 09:05:09 +00:00			`.. _cmd-switch:`

Switch command docs from \section to reStructuredText 2018-12-17 01:39:33 +00:00			`switch - conditionally execute a block of commands`
Fix command section separator line lengths 2019-01-03 04:10:47 +00:00			`==================================================`
Switch command docs from \section to reStructuredText 2018-12-17 01:39:33 +00:00
Migrate the 'synopsis' sections to .rst format 2018-12-18 01:58:24 +00:00			`Synopsis`
			`--------`
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
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 2022-01-09 14:09:46 +00:00			`.. synopsis::`

			`switch VALUE; [case [GLOB ...]; [COMMANDS ...]; ...] end`
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
Convert \\subsection sections into rst format 2018-12-19 02:44:30 +00:00			`Description`
Fix command section separator line lengths 2019-01-03 04:10:47 +00:00			`-----------`
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
More synopsis work. A great leap forward 2021-12-22 01:24:47 +00:00			``switch`` performs one of several blocks of commands, depending on whether a specified value equals one of several globbed values. ``case`` is used together with the ``switch`` statement in order to determine which block should be executed.
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
More synopsis work. A great leap forward 2021-12-22 01:24:47 +00:00			Each ``case`` command is given one or more parameters. The first ``case`` command with a parameter that matches the string specified in the switch command will be evaluated. ``case`` parameters may contain globs. These need to be escaped or quoted in order to avoid regular glob expansion using filenames.
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
			`Note that fish does not fall through on case statements. Only the first matching case is executed.`

docs: Use :doc: role when linking to commands This makes it so we link to the very top of the document instead of a special anchor we manually include. So clicking e.g. :doc:`string <cmds/string>` will link you to cmds/string.html instead of cmds/string.html#cmd-string. I would love to have a way to say "this document from the root of the document path", but that doesn't appear to work, I tried `/cmds/string`. So we'll just have to use cmds/string in normal documents and plain `string` from other commands. 2022-09-23 17:57:49 +00:00			Note that :doc:`break <break>` cannot be used to exit a case/switch block early like in other languages. It can only be used in loops.
Document that break cannot be used in switch 2022-09-17 05:12:10 +00:00
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00			`Note that command substitutions in a case statement will be evaluated even if its body is not taken. All substitutions, including command substitutions, must be performed before the value can be compared against the parameter.`


Convert \\subsection sections into rst format 2018-12-19 02:44:30 +00:00			`Example`
Fix command section separator line lengths 2019-01-03 04:10:47 +00:00			`-------`
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
docs: More about envvars 2023-01-09 19:33:37 +00:00			If the variable ``$animal`` contains the name of an animal, the following code would attempt to classify it:
Switch \fish sections to rst format 2018-12-19 03:14:04 +00:00
			`::`

			`switch $animal`
			`case cat`
			`echo evil`
			`case wolf dog human moose dolphin whale`
			`echo mammal`
			`case duck goose albatross`
			`echo bird`
			`case shark trout stingray`
			`echo fish`
			`case '*'`
			`echo I have no idea what a $animal is`
			`end`

Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
Switch backticks to double backticks for rst compatibility 2018-12-19 20:02:45 +00:00			If the above code was run with ``$animal`` set to ``whale``, the output
			would be ``mammal``.