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Mastering the `diff` Command in Linux

Linux provides a versatile tool known as diff for comparing files and directories. It helps users to identify differences between two text files line by line. Programmers often use diff to track changes in source code or configuration files.


The basic syntax of the diff command is:

diff [OPTION]... FILES
  • FILES are the two files you want to compare.
  • [OPTION]... represents the various options that can modify the behavior of diff.


Below is a table of some common options for the diff command:

--normalOutput a normal diff (default).
--briefReport only if files differ.
--side-by-side-yOutput in two columns.
--ignore-case-iIgnore case differences in file contents.
--ignore-all-space-wIgnore all whitespace.
--recursive-rRecursively compare any subdirectories found.
--unified-uOutput unified diff format.
--context-COutput diff with context.
--colorColorize the output.
--helpDisplay a help message and exit.
--versionDisplay version information and exit.

Creating Example Files

Let's create two example files to demonstrate the use of the diff command.

  1. File 1: original.txt

    vim original.txt

    Press i to switch to insert mode and enter:


    Save and exit with :wq.

  2. File 2: modified.txt

    vim modified.txt

    Add the following content:


    Save and exit with :wq.

Example 1: Basic diff

To compare two files in the normal diff format:

diff original.txt modified.txt


< Apple
> apple
< Date
> Dragonfruit

The diff output uses < to indicate lines from original.txt and > for modified.txt. The c indicates a change between the files.

Example 2: Unified Format

Unified format provides a more compact view of the changes:

diff -u original.txt modified.txt


--- original.txt
+++ modified.txt
@@ -1,4 +1,4 @@

The unified format displays a few lines of context by default, showing changes with + for additions and - for deletions.

Example 3: Side-by-Side Comparison

To compare files side by side:

diff --side-by-side original.txt modified.txt


Apple                                                  | apple
Banana Banana
Cherry Cherry
Date | Dragonfruit

The side-by-side view shows both files next to each other, with a | indicating differing lines.

Example 4: Ignoring Case

If you want to compare files but ignore case differences:

diff -i original.txt modified.txt

There will be no output if the only difference is case since -i tells diff to ignore these differences.

Example 5: Recursive Diff

To compare directories recursively, use -r. Let's assume dir1 and dir2 contain our example files:

diff -r dir1 dir2


This will list the differences between any files found in the directories and their subdirectories.

Combining diff with Other Commands

diff can be combined with other commands, such as grep or less, for more advanced operations:

diff original.txt modified.txt | less

This will pipe the output of diff to less for easy scrolling through many differences.


The diff command is a cornerstone of file comparison in Linux, crucial for users who need to track changes between file versions. Understanding its options allows for customized comparisons, fitting the needs of any user

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