fish-shell/sphinx_doc_src/cmds/isatty.rst

isatty - test if a file descriptor is a tty.
============================================

Synopsis
--------

isatty [FILE DESCRIPTOR]


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

``isatty`` tests if a file descriptor is a tty.

``FILE DESCRIPTOR`` may be either the number of a file descriptor, or one of the strings ``stdin``, ``stdout``, or ``stderr``.

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


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
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			`--------`
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			`isatty [FILE DESCRIPTOR]`
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Switch backticks to double backticks for rst compatibility 2018-12-19 20:02:45 +00:00			``FILE DESCRIPTOR`` may be either the number of a file descriptor, or one of the strings ``stdin``, ``stdout``, or ``stderr``.
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			`If the specified file descriptor is a tty, the exit status of the command is zero. Otherwise, the exit status is non-zero. No messages are printed to standard error.`


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			`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`

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			`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`