The -u option in the diff command stands for "unified" format. It provides a more compact and readable output by showing a few lines of context around the differences between two files. This format is often used for creating patch files because it makes it easier to understand the changes in the context of the surrounding lines.
When you use diff -u file1.txt file2.txt, the output will display lines that are unchanged, along with lines that have been added or removed, marked with + for additions and - for deletions.
