What is diff?

Diff is a tool that compares two pieces of text-usually files-and shows you what lines have been added, removed, or changed. Think of it like a side‑by‑side highlight that points out the differences between two versions of a document or code.

Let's break it down

  • Input: You give diff two files (or two versions of the same file).
  • Process: It reads each line and matches them up.
  • Output: It prints a list of changes using symbols (e.g., ”+” for added lines, ”‑” for removed lines) or a special format called “unified diff” that shows a few lines of context around each change.

Why does it matter?

Knowing exactly what changed helps you:

  • Track bugs by seeing what code was altered.
  • Review code before merging it into a project.
  • Keep a history of document edits.
  • Resolve conflicts when multiple people edit the same file.

Where is it used?

  • Version control systems like Git, Mercurial, and Subversion.
  • Code review tools (GitHub, GitLab, Bitbucket).
  • Patch creation for software updates.
  • Text comparison utilities in IDEs and text editors.

Good things about it

  • Fast and works on any plain‑text file.
  • Produces a clear, human‑readable list of changes.
  • Can be scripted to automate updates or generate patches.
  • Integrated into most development workflows and tools.

Not-so-good things

  • Only compares line by line; it can’t understand deeper structural changes (e.g., moved code blocks).
  • Output can be noisy for large files with many small edits.
  • Binary files need special handling; diff isn’t useful for images or compiled binaries.
  • Different diff implementations may have slightly different output formats, which can cause confusion.