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3a23fdf359
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.
42 lines
1.1 KiB
ReStructuredText
42 lines
1.1 KiB
ReStructuredText
.. _cmd-isatty:
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isatty - test if a file descriptor is a terminal
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================================================
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Synopsis
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--------
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.. synopsis::
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isatty [FILE DESCRIPTOR]
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Description
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-----------
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``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).
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``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.
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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.
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The **-h** or **--help** option displays help about using this command.
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Examples
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--------
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From an interactive shell, the commands below exit with a return value of zero::
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isatty
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isatty stdout
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isatty 2
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echo | isatty 1
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And these will exit non-zero::
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echo | isatty
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isatty 9
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isatty stdout > file
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isatty 2 2> file
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