fish-shell/doc_src/cmds/printf.rst

.. _cmd-printf:

printf - display text according to a format string
==================================================

Synopsis
--------

.. synopsis::

    printf FORMAT [ARGUMENT ...]

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

.. only:: builder_man

          NOTE: This page documents the fish builtin ``printf``.
          To see the documentation on the ``printf`` command you might have,
          use ``command man printf``.

printf uses the format string FORMAT to print the ARGUMENT arguments. This means that it takes format specifiers in the format string and replaces each with an argument.

The ``format`` argument is re-used as many times as necessary to convert all of the given arguments. So ``printf %s\n flounder catfish clownfish shark`` will print four lines.

Unlike :ref:`echo <cmd-echo>`, ``printf`` does not append a new line unless it is specified as part of the string.

It doesn't support any options, so there is no need for a ``--`` separator, which makes it easier to use for arbitrary input than ``echo``. [#]_ 

Format Specifiers
-----------------
Valid format specifiers are taken from the C library function ``printf(3)``:

- ``%d`` or ``%i``: Argument will be used as decimal integer (signed or unsigned)

- ``%o``: An octal unsigned integer

- ``%u``: An unsigned decimal integer - this means negative numbers will wrap around

- ``%x`` or ``%X``: An unsigned hexadecimal integer

- ``%f``, ``%g`` or ``%G``: A floating-point number. ``%f`` defaults to 6 places after the decimal point (which is locale-dependent - e.g. in de_DE it will be a ``,``). ``%g`` and ``%G`` will trim trailing zeroes and switch to scientific notation (like ``%e``) if the numbers get small or large enough.

- ``%e`` or ``%E``: A floating-point number in scientific (XXXeYY) notation

- ``%s``: A string

- ``%b``: As a string, interpreting backslash escapes, except that octal escapes are of the form \0 or \0ooo.

``%%`` signifies a literal "%".

Conversion can fail, e.g. "102.234" can't losslessly convert to an integer, causing printf to print an error. If you are okay with losing information, silence errors with ``2>/dev/null``.

A number between the ``%`` and the format letter specifies the width. The result will be left-padded with spaces.

Backslash Escapes
-----------------
printf also knows a number of backslash escapes:

- ``\"`` double quote
- ``\\`` backslash
- ``\a`` alert (bell)
- ``\b`` backspace
- ``\c`` produce no further output
- ``\e`` escape
- ``\f`` form feed
- ``\n`` new line
- ``\r`` carriage return
- ``\t`` horizontal tab
- ``\v`` vertical tab
- ``\ooo`` octal number (ooo is 1 to 3 digits)
- ``\xhh`` hexadecimal number (hhh is 1 to 2 digits)
- ``\uhhhh`` 16-bit Unicode character (hhhh is 4 digits)
- ``\Uhhhhhhhh`` 32-bit Unicode character (hhhhhhhh is 8 digits)

Errors and Return Status
------------------------
If the given argument doesn't work for the given format (like when you try to convert a number like 3.141592 to an integer), printf prints an error, to stderr. printf will then also return non-zero, but will still try to print as much as it can.

It will also return non-zero if no argument at all was given, in which case it will print nothing.

This printf has been imported from the printf in GNU Coreutils version 6.9. If you would like to use a newer version of printf, for example the one shipped with your OS, try ``command printf``.

Example
-------

::

    printf '%s\t%s\n' flounder fish

Will print "flounder	fish" (separated with a tab character), followed by a newline character. This is useful for writing completions, as fish expects completion scripts to output the option followed by the description, separated with a tab character.

::

    printf '%s: %d' "Number of bananas in my pocket" 42

Will print "Number of bananas in my pocket: 42", `without` a newline.

See Also
--------

- the :ref:`echo <cmd-echo>` command, for simpler output

Footnotes
---------
.. [#] In fact, while fish's ``echo`` supports ``--``, POSIX forbids it, so other implementations can't be used if the input contains anything starting with ``-``.
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-printf:`

Switch command docs from \section to reStructuredText 2018-12-17 01:39:33 +00:00			`printf - display text according to a format string`
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::`

			`printf FORMAT [ARGUMENT ...]`
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			`-----------`
docs: Document that the man pages are for our builtins For builtins that have the same name as common commands, it might not be entirely obvious that there is another page. So, for those builtins, we add a note, but only in the man pages. (exception is true and false because the note would be longer than the page, and it's fridging true and false) Fixes #8077. 2021-07-16 16:21:41 +00:00
			`.. only:: builder_man`

			NOTE: This page documents the fish builtin ``printf``.
			To see the documentation on the ``printf`` command you might have,
			use ``command man printf``.

printf: Overhaul docs 2020-05-18 17:59:45 +00:00			`printf uses the format string FORMAT to print the ARGUMENT arguments. This means that it takes format specifiers in the format string and replaces each with an argument.`
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
printf: Overhaul docs 2020-05-18 17:59:45 +00:00			The ``format`` argument is re-used as many times as necessary to convert all of the given arguments. So ``printf %s\n flounder catfish clownfish shark`` will print four lines.
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
doc: add link to echo in printf command [ci skip] 2019-10-23 15:44:59 +00:00			Unlike :ref:`echo <cmd-echo>`, ``printf`` does not append a new line unless it is specified as part of the string.
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
printf: Overhaul docs 2020-05-18 17:59:45 +00:00			It doesn't support any options, so there is no need for a ``--`` separator, which makes it easier to use for arbitrary input than ``echo``. [#]_
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
printf: Overhaul docs 2020-05-18 17:59:45 +00:00			`Format Specifiers`
			`-----------------`
			Valid format specifiers are taken from the C library function ``printf(3)``:
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
printf: Overhaul docs 2020-05-18 17:59:45 +00:00			- ``%d`` or ``%i``: Argument will be used as decimal integer (signed or unsigned)
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
docs/printf: Don't double "%" This might be a leftover from doxygen, but sphinx does not require "%%" here to print "%", so it shows %%d instead of the correct %d [ci skip] 2019-12-20 15:58:58 +00:00			- ``%o``: An octal unsigned integer
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
printf: Overhaul docs 2020-05-18 17:59:45 +00:00			- ``%u``: An unsigned decimal integer - this means negative numbers will wrap around
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
docs/printf: Don't double "%" This might be a leftover from doxygen, but sphinx does not require "%%" here to print "%", so it shows %%d instead of the correct %d [ci skip] 2019-12-20 15:58:58 +00:00			- ``%x`` or ``%X``: An unsigned hexadecimal integer
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
printf: Overhaul docs 2020-05-18 17:59:45 +00:00			- ``%f``, ``%g`` or ``%G``: A floating-point number. ``%f`` defaults to 6 places after the decimal point (which is locale-dependent - e.g. in de_DE it will be a ``,``). ``%g`` and ``%G`` will trim trailing zeroes and switch to scientific notation (like ``%e``) if the numbers get small or large enough.
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
docs/printf: Don't double "%" This might be a leftover from doxygen, but sphinx does not require "%%" here to print "%", so it shows %%d instead of the correct %d [ci skip] 2019-12-20 15:58:58 +00:00			- ``%e`` or ``%E``: A floating-point number in scientific (XXXeYY) notation
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
docs/printf: Don't double "%" This might be a leftover from doxygen, but sphinx does not require "%%" here to print "%", so it shows %%d instead of the correct %d [ci skip] 2019-12-20 15:58:58 +00:00			- ``%s``: A string
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
docs/printf: Don't double "%" This might be a leftover from doxygen, but sphinx does not require "%%" here to print "%", so it shows %%d instead of the correct %d [ci skip] 2019-12-20 15:58:58 +00:00			- ``%b``: As a string, interpreting backslash escapes, except that octal escapes are of the form \0 or \0ooo.
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			``%%`` signifies a literal "%".
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
docs: use monospace for inline code snippets more consistently 2020-10-26 18:19:05 +00:00			Conversion can fail, e.g. "102.234" can't losslessly convert to an integer, causing printf to print an error. If you are okay with losing information, silence errors with ``2>/dev/null``.
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00
Improve string pad examples and add a cross-reference The old examples were not really showcasing that it's nice for aligning text. 2020-09-28 16:42:02 +00:00			A number between the ``%`` and the format letter specifies the width. The result will be left-padded with spaces.

printf: Overhaul docs 2020-05-18 17:59:45 +00:00			`Backslash Escapes`
			`-----------------`
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00			`printf also knows a number of backslash escapes:`
printf: Overhaul docs 2020-05-18 17:59:45 +00:00
Switch backticks to double backticks for rst compatibility 2018-12-19 20:02:45 +00:00			- ``\"`` double quote
			- ``\\`` backslash
			- ``\a`` alert (bell)
			- ``\b`` backspace
			- ``\c`` produce no further output
			- ``\e`` escape
			- ``\f`` form feed
			- ``\n`` new line
			- ``\r`` carriage return
			- ``\t`` horizontal tab
			- ``\v`` vertical tab
			- ``\ooo`` octal number (ooo is 1 to 3 digits)
			- ``\xhh`` hexadecimal number (hhh is 1 to 2 digits)
			- ``\uhhhh`` 16-bit Unicode character (hhhh is 4 digits)
			- ``\Uhhhhhhhh`` 32-bit Unicode character (hhhhhhhh is 8 digits)

printf: Overhaul docs 2020-05-18 17:59:45 +00:00			`Errors and Return Status`
			`------------------------`
docs: use monospace for inline code snippets more consistently 2020-10-26 18:19:05 +00:00			`If the given argument doesn't work for the given format (like when you try to convert a number like 3.141592 to an integer), printf prints an error, to stderr. printf will then also return non-zero, but will still try to print as much as it can.`
printf: Don't print an error if not given an argument 2020-05-18 17:34:53 +00:00
			`It will also return non-zero if no argument at all was given, in which case it will print nothing.`
Switch backticks to double backticks for rst compatibility 2018-12-19 20:02:45 +00:00
printf: Overhaul docs 2020-05-18 17:59:45 +00:00			This printf has been imported from the printf in GNU Coreutils version 6.9. If you would like to use a newer version of printf, for example the one shipped with your OS, try ``command printf``.
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			`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
Switch \fish sections to rst format 2018-12-19 03:14:04 +00:00			`::`

docs: Use \ instead of \\ in examples (#7286) Instead of informing the bell character (hex 07), the example was using an escaped \ followed by x07. $ echo \\x07 \x07 $ echo \x07 $ echo \x07 \| od -a 0000000 bel nl 0000002 $ * docs: Use \u instead of \\u Instead of informing the Unicode character 慡, this example was using an escaped \ followed by u6161. $ echo \\u6161 \u6161 $ echo \u6161 慡 Before: $ string escape --style=var 'a1 b2'\\u6161 \| string unescape --style=var a1 b2\u6161 Now: $ string escape --style=var 'a1 b2'\u6161 \| string unescape --style=var a1 b2慡 2020-08-26 16:29:03 +00:00			`printf '%s\t%s\n' flounder fish`
Switch \fish sections to rst format 2018-12-19 03:14:04 +00:00
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-16 21:08:41 +00:00			`Will print "flounder fish" (separated with a tab character), followed by a newline character. This is useful for writing completions, as fish expects completion scripts to output the option followed by the description, separated with a tab character.`

Switch \fish sections to rst format 2018-12-19 03:14:04 +00:00			`::`

Incorporate most new doc changes since branch Adds most documentation changes since 72c0213d42b77b2f01223b5515669840110ea9b9 2019-02-24 23:01:16 +00:00			`printf '%s: %d' "Number of bananas in my pocket" 42`
Switch \fish sections to rst format 2018-12-19 03:14:04 +00:00
docs: use monospace for inline code snippets more consistently 2020-10-26 18:19:05 +00:00			Will print "Number of bananas in my pocket: 42", `without` a newline.
doc: add interlinks between `echo` ←→ `printf` commands 2020-03-01 12:43:14 +00:00
			`See Also`
			`--------`

			- the :ref:`echo <cmd-echo>` command, for simpler output
printf: Overhaul docs 2020-05-18 17:59:45 +00:00
			`Footnotes`
			`---------`
Fix punctuation in footnote 2021-08-10 17:46:39 +00:00			.. [#] In fact, while fish's ``echo`` supports ``--``, POSIX forbids it, so other implementations can't be used if the input contains anything starting with ``-``.