auf den Quellcode der Suche - können Sie sehen, dass es für diesen Fall überprüft (die Datei bereits geöffnet ist für das Lesen von grep
) und meldet sie, finden Sie in der SAME_INODE
Prüfung unter:
/* If there is a regular file on stdout and the current file refers
to the same i-node, we have to report the problem and skip it.
Otherwise when matching lines from some other input reach the
disk before we open this file, we can end up reading and matching
those lines and appending them to the file from which we're reading.
Then we'd have what appears to be an infinite loop that'd terminate
only upon filling the output file system or reaching a quota.
However, there is no risk of an infinite loop if grep is generating
no output, i.e., with --silent, --quiet, -q.
Similarly, with any of these:
--max-count=N (-m) (for N >= 2)
--files-with-matches (-l)
--files-without-match (-L)
there is no risk of trouble.
For --max-count=1, grep stops after printing the first match,
so there is no risk of malfunction. But even --max-count=2, with
input==output, while there is no risk of infloop, there is a race
condition that could result in "alternate" output. */
if (!out_quiet && list_files == 0 && 1 < max_count
&& S_ISREG (out_stat.st_mode) && out_stat.st_ino
&& SAME_INODE (st, out_stat))
{
if (! suppress_errors)
error (0, 0, _("input file %s is also the output"), quote (filename));
errseen = true;
goto closeout;
}
Vielen Dank für die Antwort, ich vergessen, wie die Shell setzt tatsächlich den Prozess der Datei-Deskriptoren vorher und dass grep Informationen über diese überprüfen können. – iobender
@iobender, Gern geschehen. – falsetru