ttyname, ttyname_r - return name of a terminal
#include <unistd.h>
char *ttyname(int fd);
int ttyname_r(int fd, char buf[.buflen], size_t buflen);The function ttyname() returns a pointer to the
null-terminated pathname of the terminal device that is open on the file
descriptor fd, or NULL on error (for example, if fd is
not connected to a terminal). The return value may point to static data,
possibly overwritten by the next call. The function
ttyname_r() stores this pathname in the buffer
buf of length buflen.