tail: exit without reading input if would never output

* src/tail.c (main): If -n0 or -c0 were specified without -f,
then no data would ever be output, so exit without reading input.
* tests/tail-2/tail-n0f.sh: Augment the related test with this case.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/tail.c b/src/tail.c
index ca851ee6f..cdaecddc4 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -2149,6 +2149,10 @@ main (int argc, char **argv)
                      " indefinitely is ineffective"));
   }
 
+  /* Don't read anything if we'll never output anything.  */
+  if (! n_units && ! forever && ! from_start)
+    exit (EXIT_SUCCESS);
+
   F = xnmalloc (n_files, sizeof *F);
   for (i = 0; i < n_files; i++)
     F[i].name = file[i];