Complicate truncate behavior.

1 files changed, 13 insertions, 7 deletions

diff --git a/coreutils/dd.c b/coreutils/dd.c
index a0d2330ea..32eeb661c 100644
--- a/coreutils/dd.c
+++ b/coreutils/dd.c
@@ -41,7 +41,7 @@ static struct suffix_mult dd_suffixes[] = {
 
 int dd_main(int argc, char **argv)
 {
-        int i, ifd, ofd, sync = FALSE, trunc = TRUE;
+        int i, ifd, ofd, oflag, sync = FALSE, trunc = TRUE;
         size_t in_full = 0, in_part = 0, out_full = 0, out_part = 0;
         size_t bs = 512, count = -1;
         ssize_t n;
@@ -94,8 +94,19 @@ int dd_main(int argc, char **argv)
         }
 
         if (outfile != NULL) {
-                if ((ofd = open(outfile, O_WRONLY | O_CREAT, 0666)) < 0)
+                oflag = O_WRONLY | O_CREAT;
+
+                if (!seek && trunc)
+                        oflag |= O_TRUNC;
+
+                if ((ofd = open(outfile, oflag, 0666)) < 0)
                         perror_msg_and_die("%s", outfile);
+
+                if (seek && trunc) {
+                        if (ftruncate(ofd, seek * bs) < 0)
+                                perror_msg_and_die("%s", outfile);
+                }
+
                 statusfp = stdout;
         } else {
                 ofd = STDOUT_FILENO;
@@ -113,11 +124,6 @@ int dd_main(int argc, char **argv)
                         perror_msg_and_die("%s", outfile);
         }
 
-        if (trunc) {
-                if (ftruncate(ofd, seek * bs) < 0)
-                        perror_msg_and_die("%s", outfile);
-        }
-
         while (in_full + in_part != count) {
                 n = safe_read(ifd, buf, bs);
                 if (n < 0)