GNU parallel - two parameters from array as parameter

Omitting your other parallel flags just to stay focused...

parallel --link pf ::: A B ::: C D

This will run your function first with a=A, b=C followed by a=B, b=D or

a=A b=C
a=B b=D

Without --link you get full combination like this:

a=A b=C
a=A b=D
a=B b=C
a=B b=D

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Update: As Ole Tange metioned in a comment [since deleted - Ed.] there is another way to do this: use the :::+ operator. However, there is an important difference between the two alternatives if the number of arguments is not the same in each param position. An example will illustrate.

parallel --link pf ::: A B ::: C D E output:

a=A b=C
a=B b=D
a=A b=E

parallel pf ::: A B :::+ C D E output:

a=A b=C
a=B b=D

So --link will "wrap" such that all arguments are consumed while :::+ will ignore the extra argument. (In the general case I prefer --link since the alternative is in some sense silently ignoring input. YMMV.)