I want to execute this custom command on a file from the Gnome File Browser:

hexdump -C $f > $f.dump

That would create a hexdump of the file with the file's name + .dump in the directory that the file exists in. When I say $f above I mean something that would substitute the name of the file that was opened.

So I've tried "Open with", "Use a custom command". I can't get it to work. I've tried a number of symbols in place of $f. Is it even possible?

Before you suggest getting a GUI hexdump program, this is just one example. I have the need to do this sort of thing for many terminal-type programs.

Am I the only person on Earth who wishes for a hybrid File-Browser-slash-Command-Terminal? That would be a file browser which contained a terminal pane who's current directory always matched that of the file browser. One could execute shell commands in the context of what they were viewing in the browser.