comm Command

Purpose

Selects or rejects lines common to two sorted files.

Syntax

comm [ -1 -2 -3 ] File1 File2

Description

Note: If you specify - (minus) for one of the file names, the comm command reads standard input.

The comm command reads the File1 and File2 parameters and writes, by default, a three-column output to standard output. The columns consist of:

Lines that are only in File1
Lines that are only in File2
Lines that are in both File1 and File2.

Both File1 and File2 should be sorted according to the collating sequence specified by the current National Language environment.

Flags

Item	Description
-1	Suppresses the display of the first column (lines in File1).
-2	Suppresses the display of the second column (lines in File2).
-3	Suppresses the display of the third column (lines common to File1 and File2).

Exit Status

This command returns the following exit values:

Item	Description
0	All input files were output successfully.
>0	An error occurred.

Examples

To display the lines unique to each file and common to both, enter:
```
comm things.to.do things.done
```
If the files things.to.do and things.done contain the following lists:
```
things.to.do
 
buy soap
groceries
luncheon
meeting at 3
system update
tech. review
 
things.done
 
2nd revision
interview
luncheon
system update
tech. review
weekly report
```
then the comm command displays:
```
       2nd revision
buy soap
groceries
       interview
               luncheon
meeting at 3
               system update
               tech. review
       weekly report
```
The first column contains the lines found only in things.to.do. The second column, indented with a tab character, lists the lines found only in things.done. The third column, indented with two tabs, lists the lines common to both.
To display the lines that appear in only one file, enter:
```
comm -23 things.to.do things.done
```
This suppresses the second and third columns of the comm command listing. If the files are the same as in Example 1, then the following is displayed:
```
buy soap
groceries
meeting at 3
```

File

Item	Description
/usr/bin/comm	Contains the comm command.