To make it work in linux (I'm on Ubuntu):
- the correct extension is .py - its a Python script after all
- put it into $HOME/.gimp-2.x/plug-ins folder
- change it to executable (chmod +x script.py)
- restart Gimp
Also re-check if you registered the script correctly.
Source should be something like this:
from gimpfu import *
... do your work here ...
"<Image>/Filters/Menu item/&Where it will appear",
register function information is also available from script-fu console - type this in:
>>> from gimpfu import *; help(register)
Help on function register in module gimpfu:
register(proc_name, blurb, help, author, copyright, date, label, imagetypes, params, results, function, menu=None, domain=None, on_query=None, on_run=None)
This is called to register a new plug-in.