Comparing two unsorted lists in linux, listing the unique in the second file

Question

I have 2 files with a list of numbers (telephone numbers).

I\'m looking for a method of listing the numbers in the second file that is not present in the first file.

Answer 1

This should work

comm -13 <(sort file1) <(sort file2)

It seems sort -n (numeric) cannot work with comm, which uses sort (alphanumeric) internally

f1.txt

1
2
21
50

f2.txt

1
3
21
50

21 should appear in third column

#WRONG
$ comm <(sort -n f1.txt) <(sort -n f2.txt)   
                1
2
21
        3
        21
                50

#OK
$ comm <(sort f1.txt) <(sort f2.txt)
                1
2
                21
        3
                50