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 not specified, zero is assumed.
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.
The -h or --help option displays help about using this command.
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