\section isatty isatty - test if a file or file descriptor is a tty.

\subsection isatty-synopsis Synopsis
\fish{synopsis}
isatty [FILE | DEVICE | FILE DESCRIPTOR NUMBER]
\endfish

\subsection isatty-description Description

`isatty` tests if a file or file descriptor is a tty. The argument may be in the form of a file path, device, or file descriptor number. Without an argument, `standard input` is implied.

If the resolved file descriptor is a tty, the command returns zero. Otherwise, the command exits one. 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 /dev/fd/1
\endfish

And these will exit non-zero:

\fish
echo | isatty
isatty /dev/fd/9
isatty stdout > file
isatty 2 2> file
\endfish