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comm

Compare sorted files FILE1 and FILE2 line by line.

Usage

comm [OPTION]... FILE1 FILE2

Flags

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)

  --check-order     check that the input is correctly sorted, even
                      if all input lines are pairable
  --nocheck-order   do not check that the input is correctly sorted
  --output-delimiter=STR  separate columns with STR
  --total           output a summary
  -z, --zero-terminated    line delimiter is NUL, not newline
      --help     display this help and exit
      --version  output version information and exit

Note, comparisons honor the rules specified by 'LC_COLLATE'.

Examples:
  comm -12 file1 file2  Print only lines present in both file1 and file2.
  comm -3 file1 file2  Print lines in file1 not in file2, and vice versa.

GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
Full documentation at: <https://www.gnu.org/software/coreutils/comm>
or available locally via: info '(coreutils) comm invocation'

Examples

It outputs three space-offset columns:

The first contains lines that are unique to the first file or argument
The second contains lines that are unique to the second file or argument
The third column contains lines that are shared by both files

Compare normally

Content file 1 and 2

$ cat file1
192.168.1.1
192.168.1.2
192.168.1.3
192.168.1.4
192.168.1.5

$ cat file2
192.168.1.1
192.168.1.3
192.168.1.4
192.168.1.5
192.168.1.6

$ comm file1 file2                
                192.168.1.1
192.168.1.2
                192.168.1.3
                192.168.1.4
                192.168.1.5
        192.168.1.6

When only the matching lines are at interest, use the -n switch, where n is the field number(s).

$ comm -12 file1 file2
192.168.1.1
192.168.1.3
192.168.1.4
192.168.1.5

Compare where content of lines do not directly match but are matched at other lines in file

$ cat file1      
abcd
efgh

$ cat file2
abcd
aaaa
efgh

$ comm file1 file2
        abcd
    aaaa
        efgh

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