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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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