use ldflags in local docker build

Dockerfile.build

@@ -8,4 +8,5 @@ RUN  apk add --update \
      git \
      make \
      g++ \
+     coreutils \
      libc6-compat

Makefile

@@ -40,17 +40,15 @@ endif
 _build:
 	@echo "=> building doctl via go build"
 	@echo ""
-	@mkdir -p builds
-	@cd cmd/doctl && env GOOS=$(GOOS) GOARCH=$(GOARCH) GOFLAGS=-mod=vendor \
-	  go build -o $(OUT_D)/doctl_$(GOOS)_$(GOARCH)
+	@OUT_D=${OUT_D} GOOS=${GOOS} GOARCH=${GOARCH} scripts/_build.sh
 	@echo "built $(OUT_D)/doctl_$(GOOS)_$(GOARCH)"
 
 .PHONY: native
 native: _build
 	@echo "==> build local version"
 	@echo ""
 	@mv $(OUT_D)/doctl_$(GOOS)_$(GOARCH) $(OUT_D)/doctl
-	@echo "built $(OUT_D)/doctl"
+	@echo "installed as $(OUT_D)/doctl"
 
 .PHONY: _build_linux_amd64
 _build_linux_amd64: GOOS = linux

scripts/_build.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+base="-X github.com/digitalocean/doctl."
+build="$("$DIR"/scripts/version.sh -c)"
+ldflags="${base}Build=${build}"
+
+version="$("$DIR"/scripts/version.sh -s)"
+major="$(echo "$version" | cut -d . -f1)"
+ldflags="${ldflags} ${base}Major=${major}"
+
+minor="$(echo "$version" | cut -d . -f2)"
+ldflags="${ldflags} ${base}Minor=${minor}"
+
+patch="$(echo "$version" | cut -d . -f3)"
+ldflags="${ldflags} ${base}Patch=${patch}"
+
+DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )/../"
+OUT_D=${OUT_D:-${DIR}/builds}
+mkdir -p "$OUT_D"
+
+(
+  export GOOS=${GOOS:-linux}
+  export GOARCH=${GOARCH:-amd64}
+  export GOFLAGS=-mod=vendor
+  cd cmd/doctl && go build -ldflags "$ldflags" -o "${OUT_D}/doctl_${GOOS}_${GOARCH}"
+)