Linux Programmer's Manual
isatty - test whether a file descriptor refers to a terminal
int isatty(int fd );
isatty() function tests whether fd is an open file descriptor
referring to a terminal.
isatty() returns 1 if fd is an open file descriptor referring to a
terminal; otherwise 0 is returned, and errno is set to indicate the
fd is not a valid file descriptor.
fd refers to a file other than a terminal. On some older kernels,
some types of files resulted in the error EINVAL in this case
(which is a violation of POSIX, which specifies the error
For an explanation of the terms used in this section, see
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
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