just use the rule d
the extra logic to check if your password is shorter than 7 will just slow down the cracking process (more than just testing this extra password even if its longer than 7)
EDIT:
or another idea, for 3 basic rules
: (do nothing)
d (duplicate)
'6 d (first truncate at position 6 or use 7 if you want <=7, and then duplicate this word)
the extra logic to check if your password is shorter than 7 will just slow down the cracking process (more than just testing this extra password even if its longer than 7)
EDIT:
or another idea, for 3 basic rules
: (do nothing)
d (duplicate)
'6 d (first truncate at position 6 or use 7 if you want <=7, and then duplicate this word)