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:

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)'";
}
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 ''

Output:

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().