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sphinx_doc_src/cmds/isatty.rst

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+\section isatty isatty - test if a file descriptor is a tty.
+
+\subsection isatty-synopsis Synopsis
+\fish{synopsis}
+isatty [FILE DESCRIPTOR]
+\endfish
+
+\subsection isatty-description 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.
+
+
+\subsection isatty-examples Examples
+
+From an interactive shell, the commands below exit with a return value of zero:
+
+\fish
+isatty
+isatty stdout
+isatty 2
+echo | isatty 1
+\endfish
+
+And these will exit non-zero:
+
+\fish
+echo | isatty
+isatty 9
+isatty stdout > file
+isatty 2 2> file
+\endfish