ctermid - get controlling terminal name
char *ctermid(char *s);
ctermid() returns a string which is the pathname for the
current controlling terminal for this process. If s is
NULL, a static buffer is used, otherwise s points to a
buffer used to hold the terminal pathname. The symbolic
constant L_ctermid is the maximum number of characters in
the returned pathname.
The pointer to the pathname.
The path returned may not uniquely identify the control
ling terminal; it may, for example, be /dev/tty.
It is not assured that the program can open the terminal.