comm – compare two sorted files line by line.

Usage: comm [OPTION]… FILE1 FILE2
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)

–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
–help display this help and exit
–version output version information and exit

Note, comparisons honor the rules specified by ‘LC_COLLATE’.

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:
Full documentation at:
or available locally via: info ‘(coreutils) comm invocation’

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