NAME

comm − Compares two sorted files. 

SYNOPSIS

comm [−123] file1 file2

STANDARDS

Interfaces documented on this reference page conform to industry standards as follows:

command: XCU5.0  

Refer to the standards(5) reference page for more information about industry standards and associated tags. 

OPTIONS

−1Suppresses output of the first column (lines in file1 only). 

−2Suppresses output of the second column (lines in file2 only). 

−3Suppresses output of the third column (lines common to file1 and file2). 

The command comm −123 produces no output. 

OPERANDS

file1A pathname of the first file to be compared. If file1 is a hyphen (-), the standard input is used. 

file2A pathname of the second file to be compared. If file2 is a hyphen (-), the standard input is used. 

If both file1 and file2 refer to standard input or to the same FIFO special, block special or character special file, the results are undefined. 

DESCRIPTION

The comm command reads file1 and file2 and writes three columns to standard output, showing which lines are common to the files and which are unique to each. 

The leftmost column of standard output includes lines that are in file1 only.  The middle column includes lines that are in file2 only.  The rightmost column includes lines that are in both file1 and file2. 

If you specify a hyphen (−) in place of one of the file names, comm reads standard input. 

Generally, file1 and file2 should be sorted according to the collating sequence specified by the LC_COLLATE environment variable. (See sort(1).)  If the input files are not sorted properly, the output of comm might not be useful. 

EXIT STATUS

0Successful completion. 

>0Error occurred. 

EXAMPLES

     1.In the following examples, file1 contains the following sorted list of North American cities:

Anaheim
Baltimore
Boston
Chicago
Cleveland
Dallas
Detroit
Kansas City
Milwaukee
Minneapolis
New York
Oakland
Seattle
Toronto

The second file, file2, contains this sorted list:

Atlanta
Chicago
Cincinnati
Houston
Los Angeles
Montreal
New York
Philadelphia
Pittsburgh
San Diego
San Francisco
St. Louis

To display the lines unique to each file and common to the two files, enter:

comm file1 file2

This command results in the following output:

Anaheim
Atlanta
Baltimore
Boston
Chicago
Cincinnati
Cleveland
Dallas
Detroit
Houston
Kansas City
Los Angeles
Milwaukee
Minneapolis
Montreal
New York
Oakland
Philadelphia
Pittsburgh
San Diego
San Francisco
Seattle
St. Louis
Toronto

The leftmost column contains lines in file1 only, the middle column contains lines in file2 only, and the rightmost column contains lines common to both files. 

     2.To display any one or two of the three output columns, include the appropriate flags to suppress the columns you do not want.  For example, the following command displays columns 1 and 2 only:

comm −3 file1 file2
Anaheim
       Atlanta
Baltimore
Boston
       Cincinnati
Cleveland
Dallas
Detroit
       Houston
Kansas City
       Los Angeles
Milwaukee
Minneapolis
       Montreal
Oakland
       Philadelphia
       Pittsburgh
       San Diego
       San Francisco
Seattle
       St. Louis
Toronto

The following command displays output from only the second column:

comm −13 file1 file2
Atlanta
Cincinnati
Houston
Los Angeles
Montreal
Philadelphia
Pittsburgh
San Diego
San Francisco
St. Louis

The following command displays output from only the third column:

comm −12 file1 file2
Chicago
New York

SEE ALSO

Commands:  cmp(1), diff(1), sdiff(1), sort(1), uniq(1)