Running beyond compare 3 from mercurial

Question

I need to run beyond compare using mercurial. I have tried this (in the .hgrc).

[extensions]
hgext.extdiff=

[extdiff]
cmd.vdiff = C:\Program Files (x86)\Beyond Compare 3\bcomp.exe

which works; but it causes the command (hg vdiff file_name.c) not to be completed until I exit beyond compare, which is expected.

In order to run as an independent job, I have therefore tried

cmd.vdiff = start /b "" "C:\Program Files (x86)\Beyond Compare 3\bcomp.exe"

and

cmd.vdiff = start /b "C:\Program Files (x86)\Beyond Compare 3\bcomp.exe"

and

cmd.vdiff = start /b C:\Program Files (x86)\Beyond Compare 3\bcomp.exe

but I keep getting

The file name, directory name, or volume label syntax is incorrect

Answer 1

[merge-tools]
beyondcompare3.args=$local $other $base /mergeoutput=$output /ro /lefttitle=parent1 /centertitle=base /righttitle=parent2 /outputtitle=merged /automerge /reviewconflicts /solo
beyondcompare3.premerge=False
beyondcompare3.regkey=Software\Scooter Software\Beyond Compare 3
beyondcompare3.regkeyalt=Software\Wow6432Node\Scooter Software\Beyond Compare 3
beyondcompare3.regname=ExePath
beyondcompare3.gui=True
beyondcompare3.priority=-1
beyondcompare3.diffargs=/lro /lefttitle='$plabel1' /righttitle='$clabel' /solo /expandall $parent $child
beyondcompare3.diff3args=$parent1 $parent2 $child /lefttitle='$plabel1' /centertitle='$clabel' /righttitle='$plabel2' /solo /ro
beyondcompare3.dirdiff=True
...
[ui]
merge = beyondcompare3

in mercurial.ini and both (diff|merge) operations will be executed in BC3