Prototype: difference(list1, list2)

Return type: slist

Description: Returns the unique elements in list1 that are not in list2.

This function can accept many types of data parameters.

Arguments:

  • list1: string - CFEngine base variable identifier or inline JSON - in the range: .*
  • list2: string - CFEngine filter variable identifier or inline JSON - in the range: .*

Example:

code
body common control
{
      bundlesequence => { "test" };
}

bundle agent test
{
  vars:
      "a" slist => { 1,2,3,"x" };
      "b" slist => { "x" };

      # normal usage
      "diff_between_a_and_b" slist => difference(a, b);
      "diff_between_a_and_b_str" string => join(",", diff_between_a_and_b);

      # NOTE: advanced usage!
      "mylist1" slist => { "a", "b" };
      "mylist2" slist => { "a", "b" };
      "$(mylist1)_str" string => join(",", $(mylist1));

      # Here we're going to really call difference(a,a) then difference(a,b) then difference(b,a) then difference(b,b)
      # We create a new variable for each difference!!!
      "diff_$(mylist1)_$(mylist2)" slist => difference($(mylist1), $(mylist2));
      "diff_$(mylist1)_$(mylist2)_str" string => join(",", "diff_$(mylist1)_$(mylist2)");

  reports:
      # normal usage
      "The difference between lists a and b is '$(diff_between_a_and_b_str)'";

      # NOTE: advanced usage results!
      "The difference of list '$($(mylist1)_str)' with '$($(mylist2)_str)' is '$(diff_$(mylist1)_$(mylist2)_str)'";
}

Output:

code
R: The difference between lists a and b is '1,2,3'
R: The difference of list '1,2,3,x' with '1,2,3,x' is ''
R: The difference of list '1,2,3,x' with 'x' is '1,2,3'
R: The difference of list 'x' with '1,2,3,x' is ''
R: The difference of list 'x' with 'x' is ''

History: The collecting function behavior was added in 3.9.

See also: About collecting functions, intersection().