Search all tags with string?

[3design]

Is it possible to search a file for all tags containing string 'foo' or 'Foo' and output only the tags that match the search condition? I've tried variations of the following, on the Linux command line:

exiftool -if '$All =~ /(foo)/' *tif

with a result of "1 file failed condition"

Is it possible to do this?

[Phil Harvey]

It would be possible, but rather involved, to do this with a user-defined Composite tag, but I don't have time to be more specific at the moment.

- Phil