isatty - test if a file descriptor is a tty.

Synopsis

isatty [FILE DESCRIPTOR]

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.

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