#-h- tail.r          2038 asc  6-oct-80 07:46:55
#-h- defns            160 asc  6-oct-80 07:42:55
 #   include standard symbol definitions
 #        include ratdef
 
define(MAXBUF,3000)     # line buffer size
define(DEFAULT,23)      # default if no argument
#-h- tail            1027 asc  6-oct-80 07:42:57
# tail - print tail portion of a file
 subroutine main
   character arg(MAXLINE)
   integer n, i, fd
   integer ctoi, getarg, open

   n = DEFAULT
   for (i=1; getarg(i, arg, MAXLINE) != EOF; i=i+1)
        {
        if (arg(1) == QMARK & arg(2) == EOS)
                call error ("usage:  tail [-n] [files].")
        else if (arg(1) == MINUS & arg(2) != EOS)
                {
                j = 2
                n = ctoi(arg, j)
                if (n <= 0)
                        call error ("invalid size.")
                }
        else if (arg(1) == MINUS & arg(2) == EOS)
                {
                fd = STDIN
                call ptail (n, fd)
                }
        else
                {
                fd = open(arg, READ)
                if (fd == ERR)
                        call cant(arg)
                call ptail (n, fd)
                call close(fd)
                }
        }
 
   if (fd == ERR)               #no files specified, read STDIN
        call ptail (n, STDIN)
   return
   end
#-h- ptail            704 asc  6-oct-80 07:43:00
 ## ptail - print last 'n' lines of file 'fd'
 subroutine ptail (nlins, fd)
 integer n, fd, nlins
 character buf(MAXBUF)
 character getch
 integer head, tail, i
 
   head = 1
   tail = 1
   n = nlins
   while (getch(buf(tail), fd) ^= EOF) {
      tail = mod(tail, MAXBUF) + 1
      if (tail == head)
         head = mod(head, MAXBUF) + 1
      }
   for (i = tail; i ^= head; ) {
      i = i - 1
      if (i == 0)
         i = MAXBUF
      if (buf(i) == NEWLINE) {
         n = n - 1
         if (n < 0) {
            i = mod(i, MAXBUF) + 1
            break
            }
         }
      }
   for (head = i; head ^= tail; head = mod(head, MAXBUF) + 1)
      call putch(buf(head), STDOUT)
 
 return
 end