Sorry to be replying to this so late; I hadn't noticed the post until now!

I've tried putting that code in my p4merge script and yes it does indeed work fine. However, it puts a temporary file in the working directory which I'm not sure is a good idea? If we look at this patch which actually solved pretty much the same problem, but when merging and, during a merge conflict, a file was created in both branches:

... it is creating a temp file in a proper temp dir, rather than in the working dir. I think that would be the proper solution here. However, I really want to get this fixed so I'd be happy for this band-aid fix of the p4merge script to be checked in until we could get a patch more like the aforementioned one, at a later date, to create empty files in a proper temp dir and pass them as $LOCAL and $REMOTE. :-)

Best regards,
Jeremy Morton (Jez)

On 11/10/2012 04:22, David Aguilar wrote:
p4merge does not properly handle the case where "/dev/null"
is passed as a filename.

Workaround it by creating a temporary file for this purpose.

Reported-by: Jeremy Morton<>
Signed-off-by: David Aguilar<>
Jeremy, can you test this?

  mergetools/p4merge | 25 +++++++++++++++++++++++++
  1 file changed, 25 insertions(+)

diff --git a/mergetools/p4merge b/mergetools/p4merge
index 1a45c1b..295361a 100644
--- a/mergetools/p4merge
+++ b/mergetools/p4merge
@@ -1,5 +1,30 @@
  diff_cmd () {
+       # p4merge does not like /dev/null
+       rm_local=
+       rm_remote=
+       if test "/dev/null" = "$LOCAL"
+       then
+               LOCAL="./p4merge-dev-null.LOCAL.$$"
+               >"$LOCAL"
+               rm_local=true
+       fi
+       if test "/dev/null" = "$REMOTE"
+       then
+               REMOTE="./p4merge-dev-null.REMOTE.$$"
+               >"$REMOTE"
+               rm_remote=true
+       fi
        "$merge_tool_path" "$LOCAL" "$REMOTE"
+       if test -n "$rm_local"
+       then
+               rm -f "$LOCAL"
+       fi
+       if test -n "$rm_remote"
+       then
+               rm -f "$REMOTE"
+       fi

  merge_cmd () {
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