fish-shell/doc_src/cmds/printf.rst

.. _cmd-printf:

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

Synopsis
--------

::

    printf FORMAT [ARGUMENT ...]

Description
-----------
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`.

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 17:05:09 +08:00			`.. _cmd-printf:`

Switch command docs from \section to reStructuredText 2018-12-17 09:39:33 +08:00			`printf - display text according to a format string`
Fix command section separator line lengths 2019-01-03 12:10:47 +08:00			`==================================================`
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: update all command synopsis formatting Adds synopses for those commands missing them. Moves all synopsis sections to code blocks. This improves the appearance, although highlighting as fish code may not be the ideal appearance. 2019-09-17 17:59:04 +08:00			`::`
Migrate the 'synopsis' sections to .rst format 2018-12-18 09:58:24 +08:00
docs: update all command synopsis formatting Adds synopses for those commands missing them. Moves all synopsis sections to code blocks. This improves the appearance, although highlighting as fish code may not be the ideal appearance. 2019-09-17 17:59:04 +08:00			`printf FORMAT [ARGUMENT ...]`
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			`-----------`
printf: Overhaul docs 2020-05-19 01:59:45 +08:00			`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 2018-12-17 05:08:41 +08:00
printf: Overhaul docs 2020-05-19 01:59:45 +08:00			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 2018-12-17 05:08:41 +08:00
doc: add link to echo in printf command [ci skip] 2019-10-23 23:44:59 +08:00			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 2018-12-17 05:08:41 +08:00
printf: Overhaul docs 2020-05-19 01:59:45 +08:00			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 2018-12-17 05:08:41 +08:00
printf: Overhaul docs 2020-05-19 01:59:45 +08:00			`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 2018-12-17 05:08:41 +08:00
printf: Overhaul docs 2020-05-19 01:59:45 +08:00			- ``%d`` or ``%i``: Argument will be used as decimal integer (signed or unsigned)
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00
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 23:58:58 +08:00			- ``%o``: An octal unsigned integer
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00
printf: Overhaul docs 2020-05-19 01:59:45 +08:00			- ``%u``: An unsigned decimal integer - this means negative numbers will wrap around
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00
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 23:58:58 +08:00			- ``%x`` or ``%X``: An unsigned hexadecimal integer
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00
printf: Overhaul docs 2020-05-19 01:59:45 +08:00			- ``%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 2018-12-17 05:08:41 +08:00
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 23:58:58 +08:00			- ``%e`` or ``%E``: A floating-point number in scientific (XXXeYY) notation
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00
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 23:58:58 +08:00			- ``%s``: A string
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00
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 23:58:58 +08:00			- ``%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 2018-12-17 05:08:41 +08:00
Switch backticks to double backticks for rst compatibility 2018-12-20 04:02:45 +08:00			``%%`` signifies a literal "%".
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00
printf: Overhaul docs 2020-05-19 01:59:45 +08:00			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 2018-12-17 05:08:41 +08:00
printf: Overhaul docs 2020-05-19 01:59:45 +08:00			`Backslash Escapes`
			`-----------------`
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00			`printf also knows a number of backslash escapes:`
printf: Overhaul docs 2020-05-19 01:59:45 +08:00
Switch backticks to double backticks for rst compatibility 2018-12-20 04:02:45 +08:00			- ``\"`` 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 2020-05-19 01:59:45 +08:00			`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.
printf: Don't print an error if not given an argument 2020-05-19 01:34:53 +08:00
			`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 2018-12-20 04:02:45 +08:00
printf: Overhaul docs 2020-05-19 01:59:45 +08:00			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 2018-12-17 05:08:41 +08:00
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			`::`

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

Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00			`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 11:14:04 +08:00			`::`

Incorporate most new doc changes since branch Adds most documentation changes since 72c0213d42b77b2f01223b5515669840110ea9b9 2019-02-25 07:01:16 +08:00			`printf '%s: %d' "Number of bananas in my pocket" 42`
Switch \fish sections to rst format 2018-12-19 11:14:04 +08:00
Copy doc_src to sphinx_doc_src and add a TOC 2018-12-17 05:08:41 +08:00			`Will print "Number of bananas in my pocket: 42", _without_ a newline.`
doc: add interlinks between `echo` ←→ `printf` commands 2020-03-01 20:43:14 +08:00
			`See Also`
			`--------`

			- the :ref:`echo <cmd-echo>` command, for simpler output
printf: Overhaul docs 2020-05-19 01:59:45 +08:00
			`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 `-`)