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go build — Interview Q&A

Labeled by level. Keep answers concise; expand with examples in person.

Junior

Q1. What does go build produce? For a main package, an executable on disk (named after the directory/module by default, or via -o). For a library package, nothing is written — it just type-checks the code.

Q2. How is go build different from go run? go build writes a persistent binary you run separately and reuse. go run builds to a temp location, runs once, and deletes it.

Q3. How do you name the output file? With -o: go build -o app .. The flag goes before the package path.

Q4. How do you build every package in a module? go build ./... compiles and type-checks all packages recursively.

Middle

Q5. How do you cross-compile for Linux from a Mac? Set the target env: GOOS=linux GOARCH=amd64 go build -o app .. Pure-Go programs need no extra toolchain.

Q6. How do you embed a version string at build time? go build -ldflags="-X main.version=$(git describe --tags)" ., with a package-level var version string.

Q7. What does -trimpath do and why use it? It removes absolute source paths from the binary, making builds reproducible and avoiding leaking developer home-directory paths.

Q8. Why build with CGO_ENABLED=0 for containers? It produces a fully static binary with no libc dependency, so it runs in scratch/distroless/static images.

Senior

Q9. What inputs form the build cache key? Source contents, the import graph, build/link flags, build tags, the toolchain version, and environment like GOOS/GOARCH/CGO_ENABLED. Any change creates a new cache entry.

Q10. If you change -ldflags -X version, does Go rebuild every package? No. Package compilation is cached; only the link step changes (the version stamp is a link input). That is fast and expected.

Q11. What is -buildvcs and when does it bite you? Go embeds VCS metadata (commit, dirty flag) into binaries when building from a repo. In Docker/CI without .git, the build can fail; use -buildvcs=false.

Q12. How do you make a byte-for-byte reproducible binary? CGO_ENABLED=0, -trimpath, -ldflags="-buildid=" (and stripping if desired), a pinned toolchain, and pinned dependencies (go.sum). Verify by diffing two independent builds.

Professional

Q13. How does a team guarantee identical builds across engineers and CI? Centralize flags in a Makefile/GoReleaser config (trimpath, pinned ldflags, CGO setting), pin the toolchain via GOTOOLCHAIN and the go directive, pin dependencies, and reject ad-hoc go build invocations in review.

Q14. What flags differ between debug and release builds? Debug: -gcflags="all=-N -l" to keep symbols and disable inlining for delve. Release: -ldflags="-s -w" to strip symbols and shrink size. Never ship the debug build or debug the stripped one.

Common traps

  • Expecting a binary from a library package (only main produces one).
  • Putting -o after the package path.
  • -o dir/ (directory, multiple binaries) vs -o file (single file) confusion.
  • cgo cross-compilation failing without a C cross-compiler — fix with CGO_ENABLED=0.
  • Thinking version stamping forces a full rebuild (only relinks).
  • VCS stamping failing in Docker without .git.
  • Using -a "to be safe" and destroying cache performance.