xfree86 man page for isatty

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)