Compare two sorted files line by line.

      comm [-123i] file1 file2

   -1      Suppress printing of column 1

   -2      Suppress printing of column 2

   -3      Suppress printing of column 3

   -i      Case insensitive comparison of lines

The comm utility reads file1 and file2, which should be sorted lexically, and produces three text columns as output:

 Lines only in file1; Lines only in file2; Lines in both files. 

If printing of a column is suppressed, the output will be padded with TAB characters.

Each column will have a number of tab characters prepended to it equal to the number of lower numbered columns that are being printed. For example, if column number two is being suppressed, lines printed in column number one will not have any tabs preceding them, and lines printed in column number three will have one.

The comm utility assumes that the files are lexically sorted; all characters participate in line comparisons. The filename '-' means standard input.
Collation sorting: the LANG, LC_ALL, LC_COLLATE, and LC_CTYPE environment variables affect the execution of comm as described in environ(7)

“When I'm President, I will go line by line to make sure that we are not spending money unwisely” - Barack Obama

Related macOS commands:

cmp - Compare two files
diff - Display the differences between two files
diff3 - Show differences among three files
sdiff - merge two files interactively
sort - Sort text files
uniq - Uniquify files

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