comm
comm is used to check for the common lines between two sorted files line by line. This command will produce three columns of output, each showing the lines unique to file1, the unique to file2 and the common lines between file1 and file2. This is useful for checking the common content between two files.
$ printf "apple\ntomato\n"> MyFruits.txt
$ printf "carrot\ntomato\n"> MyVegetables.txt
$ comm MyFruits.txt MyVegetables.txt
apple
carrot
tomato
Useful Options / Examples
The output of comm can be redirected into a CSV file for more convenient view and manipulate using a spreadsheet.
$ comm MyFruits.txt MyVegetables.txt > common.csv
comm -1
Suppress column 1. That is to not showing the lines unique to file1 in the output. Similarly, there are comm -2(suppressing column 2, lines unique to file2), comm -3 (suppressing column 3, lines that appear in both files).
$ printf "apple\ntomato\n"> MyFruits.txt
$ printf "carrot\ntomato\n"> MyVegetables.txt
$ comm -12 MyFruits.txt MyVegetables.txt
tomato
comm --check-order
This command reports if one of the input files is not in sorted
$ printf "apple\ntomato\n"> MyFruits.txt
$ printf "tomato\ncarrot\n"> MyVegetables.txt
$ comm --check-order MyFruits.txt MyVegetables.txt
apple
tomato
comm: file 2 is not in sorted order
comm combined usage with sort & uniq
The input file can be sorted and pipelined so that the comm command can work properly.
$ printf "apple\ntomato\norange\napple\n"> MyFruits.txt
$ printf "tomato\ncarrot\nbroccoli\n"> MyVegetables.txt
$ comm <(sort MyFruits.txt|uniq) <(sort MyVegetables.txt|uniq)
apple
broccoli
carrot
orange
tomato
‘comm -i’
The option i ignores case sensitivity.
$ printf "Apple\nBanana\n"> BigFruits.txt
$ printf "apple\nbanana\n"> SmallFruits.txt
$ comm BigFruits.txt SmallFruits.txt
apple
Apple
banana
Banana
$ comm -i BigFruits.txt SmallFruits.txt
apple
banana