\section isatty isatty - test if the specified file descriptor is a tty

\subsection isatty-synopsis Synopsis
 <tt>isatty [FILE DESCRIPTOR]</tt>

\subsection isatty-description Description
The <tt>isatty</tt> command is used to test 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 and stderr.

If the specified file descriptor is a tty, the exit status of the command is
zero, otherwise, it is non-zero.