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100 lines
3.8 KiB
ReStructuredText
100 lines
3.8 KiB
ReStructuredText
.. _cmd-printf:
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printf - display text according to a format string
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==================================================
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Synopsis
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--------
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::
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printf FORMAT [ARGUMENT ...]
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Description
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-----------
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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.
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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.
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Unlike :ref:`echo <cmd-echo>`, ``printf`` does not append a new line unless it is specified as part of the string.
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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``. [#]_
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Format Specifiers
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-----------------
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Valid format specifiers are taken from the C library function ``printf(3)``:
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- ``%d`` or ``%i``: Argument will be used as decimal integer (signed or unsigned)
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- ``%o``: An octal unsigned integer
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- ``%u``: An unsigned decimal integer - this means negative numbers will wrap around
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- ``%x`` or ``%X``: An unsigned hexadecimal integer
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- ``%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.
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- ``%e`` or ``%E``: A floating-point number in scientific (XXXeYY) notation
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- ``%s``: A string
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- ``%b``: As a string, interpreting backslash escapes, except that octal escapes are of the form \0 or \0ooo.
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``%%`` signifies a literal "%".
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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``.
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A number between the ``%`` and the format letter specifies the width. The result will be left-padded with spaces.
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Backslash Escapes
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-----------------
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printf also knows a number of backslash escapes:
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- ``\"`` double quote
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- ``\\`` backslash
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- ``\a`` alert (bell)
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- ``\b`` backspace
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- ``\c`` produce no further output
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- ``\e`` escape
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- ``\f`` form feed
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- ``\n`` new line
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- ``\r`` carriage return
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- ``\t`` horizontal tab
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- ``\v`` vertical tab
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- ``\ooo`` octal number (ooo is 1 to 3 digits)
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- ``\xhh`` hexadecimal number (hhh is 1 to 2 digits)
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- ``\uhhhh`` 16-bit Unicode character (hhhh is 4 digits)
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- ``\Uhhhhhhhh`` 32-bit Unicode character (hhhhhhhh is 8 digits)
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Errors and Return Status
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------------------------
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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.
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It will also return non-zero if no argument at all was given, in which case it will print nothing.
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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``.
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Example
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-------
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printf '%s\t%s\n' flounder fish
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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.
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::
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printf '%s: %d' "Number of bananas in my pocket" 42
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Will print "Number of bananas in my pocket: 42", `without` a newline.
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See Also
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--------
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- the :ref:`echo <cmd-echo>` command, for simpler output
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Footnotes
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---------
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.. [#] (in fact while fish's ``echo`` supports ``--``, POSIX forbids it, so other implementations can't be used if the input contains anything starting with ``-``)
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