diff

Use

diff -u old.txt new.txt

What It Does

diff shows differences between two files or streams.

Use Unified Diff By Default

diff -u before.md after.md

Unified diff is the standard format used in patches and code review. It shows nearby context, removed lines with -, and added lines with +.

Course Example

Compare source versions or generated output when debugging:

diff -u ~/src/pages/index.md ~/playground/index-copy.md

Do not start with HTML unless the bug is specifically in generated HTML. Source files are usually easier to read.

Watch Out

No output usually means the inputs match.

Docs Pointers

• Run man diff.
• Read git diff, file, and text transforms.