comm is a command-line utility in Linux that combines the functionality of the diff and cmp commands. It is used to compare two sorted files line by line and display the lines that are common, unique, or different between the two files. comm is a useful tool for finding differences or similarities between two files and is commonly used in scripting and automation tasks.
The comm command is written in C programming language and is available as part of the GNU Core Utilities package. It is open-source software and is distributed under the GNU General Public License (GPL).
Official page of comm (Combines the functionality of diff and cmp): https://www.gnu.org/software/coreutils/manual/html_node/comm-invocation.html
Installation
comm is a part of the GNU Core Utilities package, which is usually pre-installed on most Linux distributions. However, if it is not available or you need to install it on a different operating system, you can follow the steps below:
Ubuntu/Debian
sudo apt-get install coreutils
CentOS/RHEL
sudo yum install coreutils
Usage and Examples
The basic syntax of the comm command is:
comm [OPTION]... FILE1 FILE2
Here are some examples of how to use the comm command:
Example 1: Compare two sorted files and display common lines
comm file1.txt file2.txt
This command compares the two sorted files file1.txt and file2.txt and displays the lines that are common to both files.
Example 2: Compare two sorted files and display unique lines
comm -23 file1.txt file2.txt
This command compares the two sorted files file1.txt and file2.txt and displays the lines that are unique to file1.txt. The -23 option suppresses the output of common lines (-1) and lines unique to file2.txt (-2).
Example 3: Compare two sorted files and display lines that are different
comm -3 file1.txt file2.txt
This command compares the two sorted files file1.txt and file2.txt and displays the lines that are different between the two files. The -3 option suppresses the output of common lines (-1 and -2).
Similar Commands and Benefits
There are several other commands and tools available in Linux that serve a similar purpose to comm. Some of them include:
diff
diff is a command-line utility that compares two files line by line and displays the differences between them. Unlike comm, diff does not require the files to be sorted and provides a more detailed output of the differences.
cmp
cmp is a command-line utility that compares two files byte by byte and displays the first byte and line number where the files differ. It is useful for comparing binary files or large files where line-by-line comparison is not practical.
The benefits of using comm over diff or cmp include:
- Efficiency: comm is optimized for comparing sorted files and can handle large files more efficiently than diff or cmp.
- Simplicity: comm provides a simple and concise output that shows only the common, unique, or different lines between the files.
- Flexibility: comm offers various options to customize the output and suppress specific lines, making it suitable for different use cases.
Script Examples
Here are three script examples that demonstrate the usage of comm in automation:
Script 1: Find common lines between two files
#!/bin/bash
file1="file1.txt"
file2="file2.txt"
common_lines=$(comm -12 <(sort "$file1") <(sort "$file2"))
echo "Common lines between $file1 and $file2:"
echo "$common_lines"
This script compares the two files file1.txt and file2.txt and displays the lines that are common to both files.
Script 2: Find unique lines in file1.txt
#!/bin/bash
file1="file1.txt"
file2="file2.txt"
unique_lines=$(comm -23 <(sort "$file1") <(sort "$file2"))
echo "Unique lines in $file1:"
echo "$unique_lines"
This script compares the two files file1.txt and file2.txt and displays the lines that are unique to file1.txt.
Script 3: Compare two files and output differences
#!/bin/bash
file1="file1.txt"
file2="file2.txt"
diff_lines=$(comm -3 <(sort "$file1") <(sort "$file2"))
echo "Lines that are different between $file1 and $file2:"
echo "$diff_lines"
This script compares the two files file1.txt and file2.txt and displays the lines that are different between the two files.
List of comm Functions and Constants
| Function/Constant | Description |
|---|---|
| comm | The main comm command that compares two files and displays the common, unique, or different lines. |
| -1 | Suppress the output of lines unique to file1. |
| -2 | Suppress the output of lines unique to file2. |
| -3 | Suppress the output of common lines. |
| -12 | Suppress the output of lines unique to file1 and lines unique to file2. |
| -23 | Suppress the output of common lines and lines unique to file2. |
Conclusion
The comm command in Linux is a powerful tool for comparing two sorted files and finding common, unique, or different lines. It is widely used in scripting and automation tasks to identify differences or similarities between files. The simplicity, efficiency, and flexibility of comm make it a preferred choice over other similar commands like diff or cmp. Whether you are a developer, system administrator, or data analyst, comm can help you streamline your file comparison tasks and improve your productivity.
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