Context Lines & Hunks

A diff usually shows N context lines before and after each change. By default, N = 3.

If two changes are within 2 * context lines of each other, they merge into one hunk. Otherwise they're separate hunks:

File A (10 lines)
File B same except lines 2 and 8 changed

With context=3:
  Hunk 1: lines 1-5 (1, 2, 3, 4, 5; change at 2)
  Hunk 2: lines 5-10 (5, 6, 7, 8, 9, 10; change at 8)

Adjacent? Hunk 1 ends at line 5 (context for change at 2); Hunk 2 starts at line 5.
They MERGE because they touch.

Larger context = more readable but bigger diffs. Smaller = more compact but harder to grok.

Useful flags:

• git diff -U0 — no context (just changes)
• git diff -U10 — 10 lines context (very readable)
• git diff -W — show whole function for any change (diff-ignore-all-space friend)