Stay on this page for the line-by-line comparison, then jump into the matching guide or the related cron, regex, and Markdown explainers when the task expands.
A diff compares two pieces of text and shows what was added, removed, or changed. It is the mechanism behind version control history, code review, and document comparison.
Diff algorithms typically use techniques like Longest Common Subsequence (LCS) to find the minimal set of changes between two texts. Results show additions (new lines), deletions (removed lines), and modifications (changed lines). Advanced diffs can show character-level changes within modified lines.
Unified diff shows changes in a single column with +/- markers, more compact for patches. Side-by-side diff shows both versions in parallel columns, easier for visual comparison.
Most diff tools offer options to ignore whitespace changes. This is useful when comparing code with different formatting but identical logic.