On Wed, Sep 11, 2002, Muli Ben-Yehuda wrote about "Re: tail(1) and char device files":
> No, that's not it. For !S_ISREG files, tail does the equivalent of:
>
> while (read(...) > 0) {
> allocate a buffer
> add what we read to the buffer
> continue
> }
>
> That loop will only terminate when tail runs out of memory (there's an
> xmalloc() inside the loop) or when read returns 0 (EOF) or -1 (error),
> and then tail will print everything.
Why everything? It should only print the last 10 lines (by default)...
Does it really save *the entire input* in memory, without any attempt
to "forget" all lines that are not the last 10?
> Yup, as is our character device. I'll see if I can find any mentions
> of this behaviour from tail in POSIX.
Because "tail -f" is supposed to print the last 10 lines *and* then continue
to show everything else, what exactly "tail -f" does on a file that cannot
be reopened is indeed a good question...
I suppose that your suggestion (to have it be equivalent to "cat") might
be more useful than the current behavior (equivalent to "tail" without -f),
but maybe something is explicitly defined in the standard?
POSIX (or SUv3) is available online freely, by the way, so you might want
to have a look.
--
Nadav Har'El | Wednesday, Sep 11 2002, 6 Tishri 5763
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