tail: fix -c +N. Closes 4111

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 11 insertions, 3 deletions

diff --git a/coreutils/tail.c b/coreutils/tail.c
index 454c25936..43cecbd97 100644
--- a/coreutils/tail.c
+++ b/coreutils/tail.c
@@ -203,7 +203,7 @@ int tail_main(int argc, char **argv)
                 int fd = fds[i];
 
                 if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
-                        continue; /* may happen with -E */
+                        continue; /* may happen with -F */
 
                 if (nfiles > header_threshhold) {
                         tail_xprint_header(fmt, argv[i]);
@@ -252,14 +252,14 @@ int tail_main(int argc, char **argv)
                  * Used only by +N code ("start from Nth", 1-based): */
                 seen = 1;
                 newlines_seen = 0;
-                while ((nread = tail_read(fd, buf, tailbufsize-taillen)) > 0) {
+                while ((nread = tail_read(fd, buf, tailbufsize - taillen)) > 0) {
                         if (G.from_top) {
                                 int nwrite = nread;
                                 if (seen < count) {
                                         /* We need to skip a few more bytes/lines */
                                         if (COUNT_BYTES) {
                                                 nwrite -= (count - seen);
-                                                seen = count;
+                                                seen += nread;
                                         } else {
                                                 char *s = buf;
                                                 do {
diff --git a/testsuite/tail.tests b/testsuite/tail.tests
index 7140da262..305a83b15 100755
--- a/testsuite/tail.tests
+++ b/testsuite/tail.tests
@@ -14,4 +14,12 @@ testing "tail: +N with N > file length" \
         "0\n" \
         "" "qw"
 
+testing "tail: -c +N with largish N" \
+        "
+        dd if=/dev/zero bs=16k count=1 2>/dev/null | tail -c +8200 | wc -c;
+        dd if=/dev/zero bs=16k count=1 2>/dev/null | tail -c +8208 | wc -c;
+        " \
+        "8185\n8177\n" \
+        "" ""
+
 exit $FAILCOUNT