Re: more pipe questions

[Helmethead <hoshem mel comcen com au>]

On Thu, Feb 15, 2001 at 02:53:02AM +0100, Ronald Bultje wrote:
> I remember this question being asked before, but deleted it, I think...
> 
> If I write data to a file (continuously, a logfile kinda thing), how can I
> check this file for "being updated"? I now use a read-pipe and popen("cat
> file", "r"); but there's probably a better way.
> 
> Or is it maybe possible to open this logfile "continuously" so that any
> data written to it can be caught at once?
> 
> Besides that, if I put this popen("cat file", "r"); in a while-loop, my
> tasklist shows a [cat <defunc>] and the program stops there...... Any clue
> why?
> 

Why it's getting zombies (defunct processes) would be because you are not calling pclose() on each file handle. And if you want to use popen to do this, call tail -0f not cat. any updates to the file will be immediately printed with that command.

eg.

FILE *fp;
if (!(fp = popen ("tail -0f filename", "r")))
{
    perror ("popen() failed");
    exit (1);
}
printf ("Watching filename for new data\n\n");
for (;;) /* infinite loop */
{
    char buff[80];
    if (fgets (buff, 79, fp) == NULL)
    {
	if (feof (fp))
	    fprintf (stderr, "tail closed\n");
	if (ferror (fp))
	    perror ("fgets() failed");
	exit (1);
    }
    printf ("line appended to file filename: %s\n", buff);
}

yeah, gtk-ize all that.

> Ronald
>