git diff Command: Detect Changes in CI

git diff reports the differences between commits, the index, and the working tree.

In CI, diff is less about reading patches and more about answering yes-or-no questions: did anything change, which paths changed, and is the tree clean? Its flags make it scriptable.

Common flags

• --name-only - list just the changed file paths
• --name-status - list paths with their status letter (A/M/D)
• --stat - show a per-file summary of insertions and deletions
• --exit-code - exit nonzero when there are differences (zero when clean)
• --quiet - like --exit-code but suppress output
• <from>..<to> - diff between two commits or branches

Example

# Fail the job if a generated file drifted from source
make generate
if ! git diff --exit-code -- generated/; then
  echo "Generated files are stale; run make generate" >&2
  exit 1
fi

In CI

git diff --exit-code is the classic check that codegen, formatting, or lockfiles are committed: if the tree changed after running a generator, the job fails. Use --name-only to scope later steps (build only changed packages) and --stat for readable PR summaries.

Key takeaways

• git diff --exit-code gates CI on whether generated or formatted files are committed.
• --name-only feeds change-aware steps that act on just the modified paths.
• Compare branches with from..to to scope a diff to a pull request.

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