Updating jar manifest file

Updating jar manifest file

I am trying to modify the Manifest file of a jar using this post How do I
update one file in a jar without repackaging the whole jar?
I follow following steps:
jar xf jarFile META-INF/MANIFEST.MF
Update manifest file.
jar uvf jarFile META-INF/MANIFEST.MF
Command number 3 prints ignoring entry META-INF/MANIFEST.MF. When i
further check the jar file after command 3 , "META-INF/MANIFEST.MF" is
missing from jar.
I am not sure where am i going wrong. Any pointers?
EDIT: I am on windows xp platform and using cygwin.