In perforce changelists get renumbered on submission. So for e.g. when the changelist was created it would be numbered 777 , but on submission of changelist it would get renumbered to say 790.
My question is how do I get the new CL number (790) , if I know the old CL number 777 , or vice versa ?
If you really want the original changelist number, that can be retrieved from Perforce without having to embed the original changelist number in the description. You can use the -ztag command line option to get at it. And you can only get at it through the 'changes' command (as far as I know):
d:\sandbox>p4 submit -c 24510
Submitting change 24510.
Locking 1 files ...
edit //depot/testfile.txt#2
Change 24510 renamed change 24512 and submitted.
d:\sandbox>p4 -ztag changes -m1 //depot/testfile.txt
... change 24512
... time 1294249178
... user test.user
... client client-test.user
... status submitted
... oldChange 24510
... desc <enter description here>
<saved
As pointed out, it's probably not that useful. However, I did want to note that it's possible to get at it.