how to try all 2 possible permutations of a small words list ?

[Snoopy]

Assuming a known passphrase twothree for a GnuPG private key and providing a password list containing these words

  one
  two
  three

how can I make a rule for combining all these words in a maximum of, say, 2-pair combination ?

I mean, to instruct hashcat to try all of these combinations (and of course, stop if/when found a match)

  one
  two
  three
  onetwo
  twoone
  onethree
  threeone
  twothree
  threetwo

but excluding

  onetwothree 
  twoonethree
  twothreeone
  onethreetwo
  etc.

i.e. combine only 2 of them (and that's it). Or perhaps change to a maximum of 3 of them at a later stage / in other scenario etc.

The above is just a training test in order to learn what to do in a real user case, where a forgotten GnuPG private key passphrase is most likely a combination of a few possible known expressions – not that many, but enough to be too complicated to try manually all of it.

you can combine 2 wordlists on the fly with hashcat, just provide the same list twice

or take a look at princeprocessor https://github.com/hashcat/princeprocessor