Can you tell the WinMerge version number?

It's WinMerge 2.10.2.0

Ok, I'll look into this.

Ok, it needed simply replace of '/' with '\' in command line handler for paths.

The patch (also attached):

Index: Src/MergeCmdLineInfo.cpp

--- Src/MergeCmdLineInfo.cpp (revision 6170)
+++ Src/MergeCmdLineInfo.cpp (working copy)
@@ -207,11 +207,16 @@
{
String param;
bool flag;
+
while ((q = EatParam(q, param, &flag)) != 0)
{
if (!flag)
{
- // Not a flag
+ // Its not a flag so it is a path
+ // Convert paths given in Linux-style ('/' as separator) given from
+ // Cygwin to Windows style ('\' as separator)
+ string_replace(param, String(_T("/")), String(_T("\\")));
+
// If shortcut, expand it first
if (paths_IsShortcut(param.c_str()))
param = ExpandShortcut(param.c_str());

File Added: cygwin_paths.patch

The patch

Fix committed to SVN trunk:
Completed: At revision: 6175

I'll commit this fix also to 2.10 branch. So next WinMerge release(s) will have this bug fixed.

I've now committed the fix to 2.10 branch too:
Completed: At revision: 6179

So the next 2.10.4 stable release will have this bug fixed. I'm hoping 2.10.4 release happens in begin of January...

Thanks a lot for reporting this bug!

Doesn't work in 2.11.1.8, which is later than 2008-12-17...
Shouldn't it be fixed in this version?

Yes, 2.11.1.8 has the fix I made. And I tested it by opening few URLs from cygwin prompt. Can you give examples of paths that don't work, perhaps I overlooked something...

Reopening.

Ugh. I meant paths, not URLs...

A trivial example which doesn't work:
$ winmergeu /c/JavaRa.log /c/AUTOEXEC.BAT

This doesn't work either from Cygwin shell or CMD shell.

I've upgraded to 2.11.1.8 from 2.10.2.0, without restarting. Is that a possible cause (I can't restart any time soon to check)?

BTW, the following (wrong?) syntax does open these files, though:

$ winmergeu c:JavaRa.log C:AUTOEXEC.BAT

The correct syntax works:
$ winmergeu c:\JavaRa.log C:\AUTOEXEC.BAT

Thanks for the info.

Don't you need /cygdrive/ in beginning of the path? Eg. /cygdrive/c/JavaRa.log /cygdrive/c/AUTOEXEC.BAT

Hmm. WinMerge could add this 'cygdrive' prefix to the paths using / as path separator. But I'm not sure if that is good idea generally.

These "full" Cygwin paths work for me. I'm not even sure if /c/work -style paths are supported by Cygwin officially.

So closing this as fixed.