/* * Print the error indicated * in the cerror cell. */int	errno;int	sys_nerr;char	*sys_errlist[];perror(s)char *s;{	register char *c;	register n;	c = "Unknown error";	if(errno < sys_nerr)		c = sys_errlist[errno];	n = strlen(s);	if(n) {		write(2, s, n);		write(2, ": ", 2);	}	write(2, c, strlen(c));	write(2, "\n", 1);}