02-17-2009
You can first call isatty() on each file descriptor: 0, 1 to see if it is a terminal or not.
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ISATTY(3) Linux Programmer's Manual ISATTY(3)
NAME
isatty - test whether a file descriptor refers to a terminal
SYNOPSIS
#include <unistd.h>
int isatty(int fd);
DESCRIPTION
The isatty() function tests whether fd is an open file descriptor referring to a terminal.
RETURN VALUE
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
error.
ERRORS
EBADF fd is not a valid file descriptor.
EINVAL fd refers to a file other than a terminal. POSIX.1 specifies the error ENOTTY for this case.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
+----------+---------------+---------+
|Interface | Attribute | Value |
+----------+---------------+---------+
|isatty() | Thread safety | MT-Safe |
+----------+---------------+---------+
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
SEE ALSO
fstat(2), ttyname(3)
COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the
latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
Linux 2015-08-08 ISATTY(3)