[Grml] pick invalid ones from package list

[T o n g]

Hi,

I'm wondering what's the best way to pick invalid package names from a 
package list. 

I am keeping a package list of my installed packages, but over the time, 
package can be retired, obsoleted, or simple increase in version in its 
name. I just want to pick out all those invalid ones.

Thanks

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Tong (remove underscore(s) to reply)
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