这是comm命令的用途：

$ comm -3 file1 file2
0002_bcc

来自man comm：

DESCRIPTION

   Compare sorted files FILE1 and FILE2 line by line.

   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)