go run vs go build vs go install

Why this matters

These three commands do almost the same thing — but where the binary ends up and what gets cached are very different. go run compiles to a temp dir and executes once; go build produces a binary in your CWD; go install produces one in $GOPATH/bin for use as a CLI. Mixing them up wastes minutes per build. And once you understand them, the build cache (which is shared across all three) becomes the second-most-important Go performance feature after the compiler itself.

Demo

go run compiles the package to a temporary directory, runs it once, then discards the binary — a one-shot shortcut for scripts and exploratory use. go build compiles to your working directory (or a named output via -o), giving you a portable binary you can distribute or run repeatedly. go install goes further, placing the binary in $GOPATH/bin — which should be on your $PATH — making it a permanent CLI tool available anywhere on the machine. All three share the same build cache (go env GOCACHE), so after the first compile only changed packages are recompiled; a second go run on unchanged code takes milliseconds, not seconds.

Try it yourself

1. Run all three commands on the same main.go and find each output.
2. Time them with time go run main.go vs time go build && time ./main. Note which is faster on a re-run.
3. Delete the build cache with go clean -cache and run again. Note the difference — that's how much the cache buys you.
4. Build for a different OS: GOOS=linux GOARCH=amd64 go build -o hi-linux main.go and check file hi-linux. We'll do this properly in task 8.

References

• Command go
• Go build cache (design doc)
• GoReleaser