Re: tail -f problem

[Pádraig Brady]

Jim Meyering wrote:
> 
> diff --git a/src/tail.c b/src/tail.c
> @@ -1986,8 +1964,13 @@ main (int argc, char **argv)
>    size_t n_viable = 0;
>    for (i = 0; i < n_files; i++)
>      {
> -      if (STREQ (F[i].name, "-") && !F[i].ignore
> -          && 0 <= F[i].fd && S_ISFIFO (F[i].mode))
> +      bool is_a_fifo_or_pipe =
> +        (STREQ (F[i].name, "-")
> +         && !F[i].ignore
> +         && 0 <= F[i].fd
> +         && (S_ISFIFO (F[i].mode)
> +             || (HAVE_FIFO_PIPES != 1 && isapipe (F[i].fd))));
> +      if (is_a_fifo_or_pipe)
>          F[i].ignore = true;
>        else
>          ++n_viable;

Note that old code you moved down has an issue under ksh
which causes tail-2/pipe-f to fail.
I.E. this will wait under ksh for both original and new tail:

  echo foobar | POSIXLY_CORRECT="" tail -c3 -f

This seems to be because the HAVE_FIFO_PIPES compile time test,
which assumes the shell is going to call pipe().
BTW, tail is the only coreutils user of isapipe().

Could tail in this case just do:

S_ISFIFO (F[i].mode) || S_ISSOCK (F[i].mode)

I'm not sure about the general isapipe() case.

cheers,
Pádraig.