comm женужно было сравнить все строки одного файла со строками другого и записать полные дубли в третий файл.
NAME
comm - compare two sorted files line by line
SYNOPSIS
comm [OPTION]... FILE1 FILE2
DESCRIPTION
Compare sorted files FILE1 and FILE2 line by line.
When FILE1 or FILE2 (not both) is -, read standard input.
With no options, produce three-column output. Column one contains lines unique to
FILE1, column two contains lines unique to FILE2, and column three contains lines
common to both files.
-1 suppress column 1 (lines unique to FILE1)
-2 suppress column 2 (lines unique to FILE2)
-3 suppress column 3 (lines that appear in both files)