commandliners

Given two ordered files, like

$ cat foo
abbreviation
carnivore
meal
topology

and

$ cat bar
aristide
meal
nap
scout
topology
zero

comm prints, in succession and in a three-column format, the lines corresponding exclusively to the first file (first column), exclusively to the second file (second column) and to both of them (third column). Thus,

$ comm foo bar
abbreviation
        aristide
carnivore
                meal
        nap
        scout
                topology
        zero

CL options are -f (fold case in comparison) and any (or several) of -1, -2, -3, which suppresses the output of column 1, 2 and/or 3. So, in above’s example,

$ comm -2 foo bar
abbreviation
carnivore
        meal
        topology

For example, if you want to get rid of some words in your dictionary, you may do

$ comm -13 - foo > foo.without.topology
topology
^d
$ cat foo.without.topology
abbreviation
carnivore
meal

More useful than one can think at first.