I want to know whether linux has got a clipboard available globally, ie, in
the inter-application (is it the correct word to use??) level for the shell
environment.

I have seen clipboard plugin icons (where i can select the current active
clip from among the previous clips) with kde and gnome. Do they r specific
to the particular window manager? If then, there can be some shell specific
clipboard thing available too, ha??

Do all these environments use some file lurking somewhere in my home
directory as the clipboard database??

>Do all these environments use some file lurking somewhere in my home
directory as the clipboard database??

In the case of X environments: No, I believe it happens in memory.

As for getting clipboardish functionality at a linux terminal, you might try gpm.