isatty(3) - NetBSD Manual Pages

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TTYNAME(3)              NetBSD Library Functions Manual             TTYNAME(3)


NAME

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


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <unistd.h>

     char *
     ttyname(int fd);

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

     int
     isatty(int fd);

     #include <stdlib.h>

     int
     ttyslot();


DESCRIPTION

     These functions operate on the system file descriptors for terminal type
     devices.  These descriptors are not related to the standard I/O FILE
     typedef, 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)), or for pseudo-terminal devices created in ptyfs
     and named /dev/pts/n.

     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() is the reentrant version of
     the above, and it places the results in buf.  If there is not enough
     space to place the results (indicated by len), then it returns an error.

     The ttyslot() function fetches the current process' control terminal num-
     ber from the ttys(5) file entry.  If the terminal is a pseudo-terminal,
     and there is no special entry in the ttys(5) file for it, the slot number
     returned is 1 + (last slot number) + minor(tty).  This will return a con-
     sistent and unique number for each pseudo-terminal device without requir-
     ing one to enumerate all of them in ttys(5).


IMPLEMENTATION NOTES

     As an optimisation, these functions attempt to obtain information about
     all devices from the /var/run/dev.db database, if it exists.  If the
     database exists but is out of date, then these functions may produce
     incorrect results.  The database should be updated using the dev_mkdb(8)
     command.


RETURN VALUES

     The ttyname() function returns the NUL-terminated name if the device is
     found and isatty() is true; otherwise a NULL pointer is returned and
     errno is set to indicate the error.

     The ttyname_r() functions returns 0 on success and an error code on fail-
     ure.

     The isatty() function returns 1 if fd is associated with a terminal
     device; otherwise it returns 0 and errno is set to indicate the error.

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


FILES

     /dev/*
     /etc/ttys


ERRORS

     The ttyname(), ttyname_r(), and isatty() functions will fail if:

     [EBADF]            The fd argument is not a valid file descriptor.

     [ENOTTY]           The fd argument does not refer to a terminal device.

     The ttyname_r() function will also fail if:

     [ERANGE]           The buffer provided is not large enough to fit the
                        result.

     [ENOENT]           The terminal device is not found.  This can happen if
                        the device node has been removed after it was opened.


SEE ALSO

     ioctl(2), ttys(5), dev_mkdb(8)


STANDARDS

     The ttyname() and isatty() functions conform to ISO/IEC 9945-1:1990
     (``POSIX.1'').


HISTORY

     isatty(), ttyname(), and ttyslot() functions appeared in Version 7 AT&T
     UNIX.


BUGS

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

NetBSD 5.1.2                     June 25, 2008                    NetBSD 5.1.2