ultrix man page for isatty

ttyname(3)						     Library Functions Manual							ttyname(3)

Name
       ttyname, isatty, ttyslot - find terminal name

Syntax
       char *ttyname(filedes)

       isatty(filedes)

       ttyslot()

Description
       The subroutine returns a pointer to the null-terminated path name of the terminal device associated with file descriptor filedes (this is a
       system file descriptor and has nothing to do with the standard I/O FILE typedef).

       The subroutine returns 1 if filedes is associated with a terminal device, 0 otherwise.

       The subroutine returns the number of the entry in the file for the control terminal of the current process.

Restrictions
       The return value points to static data whose content is overwritten by each call.

Diagnostics
       The subroutine returns a null pointer (0) if filedes does not describe a terminal device in directory

       The subroutine returns 0 if is inaccessible or if it cannot determine the control terminal.

Files
       /dev/*
       /etc/ttys

See Also
       ioctl(2), ttys(5)

																	ttyname(3)