Comm command is used to compare two sorted files line by line.
syntax: comm [OPTION]... FILE1 FILE2
This command will display the lines unique in file1, lines unique in file2, and lines common to both file1 and file2 as shown below.
In the below example,
- First column displays the lines unique in file1 ( i.e name_list.txt )
- Second column displays the lines unique in file2 ( i.e name_list_new.txt )
- Third column displays the lines that are common in both the files.
$ cat name_list.txt Bram Moolenaar Ken Thompson Linus Torvalds $ cat name_list_new.txt Bram Moolenaar Dennis Ritchie Richard Stallman $ comm name_list.txt name_list_new.txt Bram Moolenaar Dennis Ritchie Ken Thompson Linus Torvalds Richard Stallman
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The real power of comm comes with the OPTIONS not explained above. The comm command can exclude columns of the output using -1, -2, or -3 where the numbers correspond to the columns described above. So to see only the lines that are in file1 but not in file2, you would run comm -23 file1 file2. Similarly to see only the lines that are in file2 but not file1, run comm -13 file1 file2. And finally, to see only the files common to both files, run comm -12 file1 file2.