Allow tar -T /dev/null to create an empty archive.

Author: landley

tests/tar.test

@@ -43,6 +43,8 @@ testing "-T newline" "$TAR -T input | LST" \
   "-rw-rw-r-- root/sys 0 2009-02-13 23:31 file1\n-rw-rw-r-- root/sys 0 2009-02-13 23:31 file2\n" "file1\nfile2\n" ""
 testing "-T null" "$TAR --null -T input | LST" \
   "-rw-rw-r-- root/sys 0 2009-02-13 23:31 file1\n-rw-rw-r-- root/sys 0 2009-02-13 23:31 file2\n" "file1\0file2\0" ""
+testing "empty -T creates empty tarball" "tar c | SUM 2" \
+  "da39a3ee5e6b4b0d3255bfef95601890afd80709\n" "" ""
 
 # User "root" is UID 0 and group "sys" is GID 3 (on Linux, BSD, and Mac),
 # inherited from Bell Labs Unix v7

toys/posix/tar.c

@@ -1045,7 +1045,7 @@ void tar_main(void)
 
   // If include file list empty, don't create empty archive
   if (FLAG(c)) {
-    if (!TT.incl) error_exit("empty archive");
+    if (!TT.incl && !FLAG(T)) error_exit("empty archive");
     TT.fd = 1;
   }
 
@@ -1194,7 +1194,7 @@ void tar_main(void)
       close(TT.fd);
       TT.fd = pipefd[0];
     }
-    do {
+    if (dl) do {
       TT.warn = 1;
       dirtree_flagread(dl->data,
         DIRTREE_SYMFOLLOW*FLAG(h)|DIRTREE_BREADTH*(FLAG(sort)|FLAG(s)),