fish-shell/doc_src/cmds/isatty.rst

.. _cmd-isatty:

isatty - test if a file descriptor is a terminal
================================================

Synopsis
--------

.. synopsis::

    isatty [FILE DESCRIPTOR]

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

``isatty`` tests if a file descriptor is a terminal (as opposed to a file). The name is derived from the system call of the same name, which for historical reasons refers to a teletypewriter (TTY).

``FILE DESCRIPTOR`` may be either the number of a file descriptor, or one of the strings ``stdin``, ``stdout``, or ``stderr``. If not specified, zero is assumed.

If the specified file descriptor is a terminal device, the exit status of the command is zero. Otherwise, the exit status is non-zero. No messages are printed to standard error.

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

Examples
--------

From an interactive shell, the commands below exit with a return value of zero::

    isatty
    isatty stdout
    isatty 2
    echo | isatty 1


And these will exit non-zero::

    echo | isatty
    isatty 9
    isatty stdout > file
    isatty 2 2> file
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-isatty:`

docs: update isatty documentation to refer to terminals Use language that is more accurate, similar to what glibc uses. Closes #6355. 2019-11-26 10:18:16 +00:00			`isatty - test if a file descriptor is a terminal`
			`================================================`
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::`

			`isatty [FILE DESCRIPTOR]`
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
docs: update isatty documentation to refer to terminals Use language that is more accurate, similar to what glibc uses. Closes #6355. 2019-11-26 10:18:16 +00:00			``isatty`` tests if a file descriptor is a terminal (as opposed to a file). The name is derived from the system call of the same name, which for historical reasons refers to a teletypewriter (TTY).
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
docs/isatty: Mention default value for FILE DESCRIPTOR As seen in share/functions/isatty.fish (note the empty string): switch "$argv" case stdin '' set fd 0 2020-09-05 05:24:39 +00:00			``FILE DESCRIPTOR`` may be either the number of a file descriptor, or one of the strings ``stdin``, ``stdout``, or ``stderr``. If not specified, zero is assumed.
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
docs: update isatty documentation to refer to terminals Use language that is more accurate, similar to what glibc uses. Closes #6355. 2019-11-26 10:18:16 +00:00			`If the specified file descriptor is a terminal device, the exit status of the command is zero. Otherwise, the exit status is non-zero. No messages are printed to standard error.`
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
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. 2022-03-11 16:18:41 +00:00			`The -h or --help option displays help about using this command.`
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			`Examples`
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
Update synopsis of a few stragglers. 2021-12-25 00:15:40 +00:00			`From an interactive shell, the commands below exit with a return value of zero::`
Switch \fish sections to rst format 2018-12-19 03:14:04 +00:00
			`isatty`
			`isatty stdout`
			`isatty 2`
			`echo \| isatty 1`

Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
Update synopsis of a few stragglers. 2021-12-25 00:15:40 +00:00			`And these will exit non-zero::`
Switch \fish sections to rst format 2018-12-19 03:14:04 +00:00
			`echo \| isatty`
			`isatty 9`
			`isatty stdout > file`
			`isatty 2 2> file`