Master Linux diff: Compare Files and Directories with Real‑World Examples

When you need to see what changed between two files or two versions of the same file, the Linux diff command provides a quick line‑by‑line comparison. The article demonstrates the command with concrete examples.

Creating sample files

First, open a terminal and create two identical files using nano: $ nano diffsample1 Enter the three lines:

发布 优质的 技术文章

Save and exit with Ctrl+X. Then create the second file: $ nano diffsample2 Enter the same three lines and save.

Basic diff usage

Run: $ diff diffsample1 diffsample2 No output means the files are identical.

Detecting a change

Edit diffsample2 changing the word 文章 to 帖子 and save.

Run diff again: $ diff diffsample1 diffsample2 The output shows 3c3, indicating line 3 in the first file should be replaced, and displays the differing words.

Understanding diff symbols

c : change

a : add

d : delete

The numbers before the letters refer to line numbers in the first file; the numbers after refer to the second file. The < and > symbols show the original and new lines respectively.

Swapping file order

Running diff diffsample2 diffsample1 reverses the reference file, so the output now suggests changing 技术帖子 back to 技术文章 .

Case‑sensitivity

If only the case of a word differs, diff reports it. Use the -i option to ignore case: $ diff -i diffsample1 diffsample2 No output means the files are considered identical when case is ignored.

Unified format and whitespace handling

Use -u for unified diff output, which prefixes removed lines with - and added lines with +:

To ignore spaces and tabs, add -w: $ diff -w diffsample1 diffsample2 After inserting extra spaces/tabs in diffsample2, the plain diff shows differences, but diff -w produces no output.

Further options

Many other flags exist for fine‑grained control; consult the manual with man diff for a complete list.