We no longer have two doc systems, move sphinx_doc_src back to doc_src

doc_src/cmds/isatty.rst

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+.. _cmd-isatty:
+
+isatty - test if a file descriptor is a terminal
+================================================
+
+Synopsis
+--------
+
+::
+
+    isatty [FILE DESCRIPTOR]
+
+Description
+-----------
+
+``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).
+
+``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 terminal device, 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
+