isatty man page on BSDi

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TTYNAME(3)		    BSD Programmer's Manual		    TTYNAME(3)

NAME
     ttyname, ttyname_r, isatty, ttyslot - get name of associated terminal
     (tty) from file descriptor

SYNOPSIS
     #include <unistd.h>

     char *
     ttyname(int fd);

     int
     ttyname_r(int fd, char *buf, size_t size);

     int
     isatty(int fd);

     int
     ttyslot(void);

DESCRIPTION
     These functions operate on the system file descriptors for terminal type
     devices. These descriptors are not related to the standard I/O FILE type-
     def, but refer to the special device files found in /dev and named
     /dev/ttyxx and for which an entry exists in the initialization file
     /etc/ttys. (See ttys(5).)

     The isatty() function determines if the file descriptor fd refers to a
     valid terminal type device.

     The ttyname() function gets the related device name of a file descriptor
     for which isatty() is true.

     The ttyname_r() function is a reentrant version of the traditional
     ttyname() function that fills in a supplied buffer buf of the given size,
     which should be at least TTY_NAME_MAX characters long.

     The ttyslot() function fetches the current process' control terminal num-
     ber from the ttys(5) file entry.

RETURN VALUES
     The ttyname() function returns the null terminated name if the device is
     found and isatty() is true; otherwise a NULL pointer is returned.

     The ttyname_r() function returns 0 on success, or the reason for failure
     (see ERRORS).  (In no case is the global variable errno changed.)

     The ttyslot() function returns the unit number of the device file if
     found; otherwise the value zero is returned.

ERRORS
     [EBADF]   The fd argument to ttyname() or ttyname_r() is invalid.

     [ENOTTY]  The fd argument to ttyname() or ttyname_r() does not refer to a
	       tty.

     [ENOENT]  While the fd argument to ttyname() or ttyname_r() appears to
	       refer to a tty, no name could be found for it.

     [ERANGE]  The buffer supplied to ttyname_r() is too small to hold the
	       name.  (That is, the supplied size does not provide sufficient
	       room.)

FILES

     /dev/*
     /etc/ttys

SEE ALSO
     ioctl(2),	ttys(5)

HISTORY
     The isatty(), ttyname(), and ttyslot() functions appeared in Version 7
     AT&T UNIX.	 The ttyname(), ttyname_r() and isatty() functions conform to
     IEEE Std1003.1-1996 (``POSIX'').

BUGS
     The ttyname() function leaves its result in an internal static object and
     returns a pointer to that object. Subsequent calls to ttyname() will mod-
     ify the same object.

     The ttyname(), isatty(), and ttyslot() functions may not be safely called
     concurrently from multiple threads, e.g., the interfaces described by
     pthreads(3).

BSDI BSD/OS			 June 4, 1993				     2
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