usage = '''fishdescriptor [-p|--pid] <pid> <action>... [-p|--pid <pid> <action>...]
<action>s
- [<here-0fd>=]<there-fd>
+ [<here-fd>=]<there-fd>
fish the openfile referenced by descriptor <there-fd> in
(the most recent) <pid> and keep a descriptor onto it;
and, optionally, give it the number <here-fd> for exec