Apr 19, 2025

How to Use the diff Command in Linux?

Understanding the `diff` Command in Linux

The diff command is an essential utility for comparing files and directories in Unix and Unix-like operating systems. It helps identify differences between files or the contents of directories, making it invaluable for developers, system administrators, and anyone needing to track changes.

Basic Usage

To compare two files, use the following command:

diff old_file new_file

This command lists the changes required to turn old_file into new_file, displaying results in a straightforward text format.

Ignoring Whitespace

Sometimes, you may want to ignore trivial changes, such as spaces or tabs. To do this, you can add the -w or --ignore-all-space option:

diff [-w|--ignore-all-space] old_file new_file

This option allows you to focus on more significant differences without being distracted by whitespace variations.

Side-by-Side Comparison

For a more visual approach, you can view differences side-by-side using the -y or --side-by-side option:

diff [-y|--side-by-side] old_file new_file

This format places the files next to each other, making it easier to spot differences at a glance.

Unified Format

Another useful option is the unified format, which presents differences in a way similar to git diff:

diff [-u|--unified] old_file new_file

This format is particularly popular among developers, as it provides context for the changes, showing surrounding lines to clarify differences.

Recursive Directory Comparison

To compare two directories and see how they differ, use the recursive option with:

diff [-r|--recursive] old_directory new_directory

This command shows names for differing files and directories as well as details about changes made to the files within.

Brief Comparison of Directories

If you only want to know which files differ between two directories without detailing the changes, use the following command:

diff [-r|--recursive] [-q|--brief] old_directory new_directory

This option will give you a concise overview of differing files without extra detail.

Creating Patch Files

With diff, you can also create a patch file that captures the differences between two text files, including handling nonexistent files as empty:

diff [-a|--text] [-u|--unified] [-N|--new-file] old_file new_file > diff.patch

This patch file can be beneficial for version control systems or sharing changes.

Color Output and Minimizing Differences

To enhance readability and approach differences more strategically, you might want to visualize the output in color or minimize the changes detected:

diff [-d|--minimal] --color=always old_file new_file

This feature helps you not only see changes clearly but also focuses on finding the smallest, most meaningful set of differences.

Conclusion

The diff command is a powerful tool for anyone needing to compare files or directories in Linux. Whether you’re managing version control, collaborating with others, or simply tracking changes, mastering diff can save time and improve your workflow. For more details, refer to the official documentation at manned.org/diff.