fish-shell/doc_src/cmds/for.rst

.. _cmd-for:

for - perform a set of commands multiple times
==============================================

Synopsis
--------

.. synopsis::

    for VARNAME in [VALUES ...]; COMMANDS ...; end

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

**for** is a loop construct. It will perform the commands specified by *COMMANDS* multiple times. On each iteration, the local variable specified by *VARNAME* is assigned a new value from *VALUES*. If *VALUES* is empty, *COMMANDS* will not be executed at all. The *VARNAME* is visible when the loop terminates and will contain the last value assigned to it. If *VARNAME* does not already exist it will be set in the local scope. For our purposes if the **for** block is inside a function there must be a local variable with the same name. If the **for** block is not nested inside a function then global and universal variables of the same name will be used if they exist.

Much like :doc:`set <set>`, **for** does not modify $status, but the evaluation of its subordinate commands can.

The **-h** or **--help** option displays help about using this command.

Example
-------

::

    for i in foo bar baz; echo $i; end
    
    # would output:
    foo
    bar
    baz


Notes
-----

The ``VARNAME`` was local to the for block in releases prior to 3.0.0. This means that if you did something like this:

::

    for var in a b c
        if break_from_loop
            break
        end
    end
    echo $var


The last value assigned to ``var`` when the loop terminated would not be available outside the loop. What ``echo $var`` would write depended on what it was set to before the loop was run. Likely nothing.
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 17:05:09 +08:00			`.. _cmd-for:`

doc: homogenize commands titles 2020-03-31 23:37:38 +08:00			`for - perform a set of commands multiple times`
			`==============================================`
Switch command docs from \section to reStructuredText 2018-12-17 09:39:33 +08:00
Migrate the 'synopsis' sections to .rst format 2018-12-18 09:58:24 +08:00			`Synopsis`
			`--------`
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00
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 22:09:46 +08:00			`.. synopsis::`

			`for VARNAME in [VALUES ...]; COMMANDS ...; end`
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00
Convert \\subsection sections into rst format 2018-12-19 10:44:30 +08:00			`Description`
Fix command section separator line lengths 2019-01-03 12:10:47 +08:00			`-----------`
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00
doc_src: Continue the slog through the letter F. We are using only :: in a synopsis for fishscript examples given of the command being documented. 2021-12-18 07:16:47 +08:00			for is a loop construct. It will perform the commands specified by COMMANDS multiple times. On each iteration, the local variable specified by VARNAME is assigned a new value from VALUES. If VALUES is empty, COMMANDS will not be executed at all. The VARNAME is visible when the loop terminates and will contain the last value assigned to it. If VARNAME does not already exist it will be set in the local scope. For our purposes if the for block is inside a function there must be a local variable with the same name. If the for block is not nested inside a function then global and universal variables of the same name will be used if they exist.
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00
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. 2022-09-24 01:57:49 +08:00			Much like :doc:`set <set>`, for does not modify $status, but the evaluation of its subordinate commands can.
Document that a for-loop passes through any exit status Unlike in other shells, for-loops do not set $status if 1. the loop count is zero, or if 2. the loop body consists of only commands like "set" that don't set $status. POSIX for-loops always set an exit status (they set 0 if no loop iterations). Following that would be awkward because it would add a lot of complexity in combination with the 2 special cases above. Document that "for" behaves the same as "set": it will pass through existing $status, and also the last child's $status. See the discussion in #8409 2021-11-18 21:27:44 +08:00
docs: omnibus cleanup Includes harmonizing the display of options and arguments, standardising terminology, using the envvar directive more broadly, adding help options to all commands that support them, simplifying some language, and tidying up multiple formatting issues. string documentation is not changed. 2022-03-12 00:18:41 +08:00			`The -h or --help option displays help about using this command.`

Convert \\subsection sections into rst format 2018-12-19 10:44:30 +08:00			`Example`
Fix command section separator line lengths 2019-01-03 12:10:47 +08:00			`-------`
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00
Switch \fish sections to rst format 2018-12-19 11:14:04 +08:00			`::`

			`for i in foo bar baz; echo $i; end`

			`# would output:`
			`foo`
			`bar`
			`baz`

Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00
Convert \\subsection sections into rst format 2018-12-19 10:44:30 +08:00			`Notes`
Fix command section separator line lengths 2019-01-03 12:10:47 +08:00			`-----`
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00
Switch backticks to double backticks for rst compatibility 2018-12-20 04:02:45 +08:00			The ``VARNAME`` was local to the for block in releases prior to 3.0.0. This means that if you did something like this:
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00
Switch \fish sections to rst format 2018-12-19 11:14:04 +08:00			`::`

			`for var in a b c`
			`if break_from_loop`
			`break`
			`end`
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00			`end`
Switch \fish sections to rst format 2018-12-19 11:14:04 +08:00			`echo $var`

Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00
Switch backticks to double backticks for rst compatibility 2018-12-20 04:02:45 +08:00			The last value assigned to ``var`` when the loop terminated would not be available outside the loop. What ``echo $var`` would write depended on what it was set to before the loop was run. Likely nothing.