Improve build script

* Use single gox command to parallelize build.
* Automatically package any archs gox spits out.
* Add sha256sums for packages.

.gitignore

@@ -3,6 +3,7 @@ coverage.out
 dist/
 pkg/
 src/
+.build/
 .DS_Store
 .idea
 *.rdb

build-github-binaries.sh

@@ -1,4 +1,11 @@
-#!/usr/bin/env sh
+#!/usr/bin/env bash
+
+set -u -e -o pipefail
+
+if [[ -z "${DRONE_TAG}" ]] ; then
+  echo 'ERROR: Missing DRONE_TAG env'
+  exit 1
+fi
 
 echo "Building binaries for Github"
 echo ""
@@ -8,22 +15,33 @@ echo  "GO_LDFLAGS: $GO_LDFLAGS"
 
 go get github.com/mitchellh/gox
 go get github.com/tcnksm/ghr
+if [[ -f 'go.mod' ]] ; then
+  go mod tidy
+fi
 
-gox -rebuild --osarch="darwin/amd64"  -ldflags "$GO_LDFLAGS" -output "dist/redis_exporter" && cd dist && tar -cvzf redis_exporter-$DRONE_TAG.darwin-amd64.tar.gz redis_exporter && rm redis_exporter && cd ..
-gox -rebuild --osarch="darwin/386"    -ldflags "$GO_LDFLAGS" -output "dist/redis_exporter" && cd dist && tar -cvzf redis_exporter-$DRONE_TAG.darwin-386.tar.gz   redis_exporter && rm redis_exporter && cd ..
-gox -rebuild --osarch="linux/amd64"   -ldflags "$GO_LDFLAGS" -output "dist/redis_exporter" && cd dist && tar -cvzf redis_exporter-$DRONE_TAG.linux-amd64.tar.gz  redis_exporter && rm redis_exporter && cd ..
-gox -rebuild --osarch="linux/386"     -ldflags "$GO_LDFLAGS" -output "dist/redis_exporter" && cd dist && tar -cvzf redis_exporter-$DRONE_TAG.linux-386.tar.gz    redis_exporter && rm redis_exporter && cd ..
-gox -rebuild --osarch="netbsd/amd64"  -ldflags "$GO_LDFLAGS" -output "dist/redis_exporter" && cd dist && tar -cvzf redis_exporter-$DRONE_TAG.netbsd-amd64.tar.gz redis_exporter && rm redis_exporter && cd ..
-gox -rebuild --osarch="netbsd/386"    -ldflags "$GO_LDFLAGS" -output "dist/redis_exporter" && cd dist && tar -cvzf redis_exporter-$DRONE_TAG.netbsd-386.tar.gz   redis_exporter && rm redis_exporter && cd ..
-gox -rebuild --osarch="windows/amd64" -ldflags "$GO_LDFLAGS" -output "dist/redis_exporter" && cd dist && zip -9    redis_exporter-$DRONE_TAG.windows-amd64.zip   redis_exporter.exe && rm redis_exporter.exe && cd ..
-gox -rebuild --osarch="windows/386"   -ldflags "$GO_LDFLAGS" -output "dist/redis_exporter" && cd dist && zip -9    redis_exporter-$DRONE_TAG.windows-386.zip     redis_exporter.exe && rm redis_exporter.exe && cd ..
+gox -rebuild -output '.build/{{.OS}}-{{.Arch}}/{{.Dir}}'
+
+mkdir -p dist
+for build in $(ls .build); do
+  echo "Creating archive for ${build}"
+  if [[ "${build}" =~ ^windows-.*$ ]] ; then
+    # Make sure to clear out zip files to prevent zip from appending to the archive.
+    rm "dist/redis_exporter-${DRONE_TAG}.${build}.zip"
+    cd ".build/${build}" && zip --quiet -9 "../../dist/redis_exporter-${DRONE_TAG}.${build}.zip" 'redis_exporter.exe' && cd ../../
+  else
+    tar -C ".build/${build}" -czf "dist/redis_exporter-${DRONE_TAG}.${build}.tar.gz" 'redis_exporter'
+  fi
+done
 
 echo "Upload to Github"
 
 pwd
 ls -la 
 ls -la dist/
 
-ghr -u oliver006 -r redis_exporter --replace $DRONE_TAG dist/
+cd dist
+sha256sum *.gz *.zip > sha256sums.txt
+
+ghr -u oliver006 -r redis_exporter --replace "${DRONE_TAG}" ./
 
 echo "Done"