parse emty multiply options

README.md

@@ -46,6 +46,7 @@ The `puppet` and the `python` image are build as they are. The php image will ge
 
 **NOTE**: For values in `multiply`, `append`, and `namespace` one may choose to use environment variables. Substition is handled by [drone/envsubst](https://github.com/drone/envsubst)
 
+The `multiply` can have an empty string as field. This wont be added to the images tag. Useful for default options. You can use Bash Syntax to use a default value instead: `echo ${MESSAGE}:-default`.
 
 ```yaml
 # docker-matrix.yml
@@ -56,6 +57,9 @@ multiply:
   OS:
     - alpine
     - debian
+  COMMAND:
+    - sleep 1y
+    - ""
 
 append:
   - { NAME: test, LANG: ${LANG} }

main.go

@@ -289,7 +289,12 @@ ARGUMENTS:
 			tag = "latest"
 		}
 		for _, key := range keyOrder {
-			tag = fmt.Sprintf("%s-%s", tag, scenario[key])
+			t := scenario[key]
+			if t == "" {
+				log.Debugf("%s skipping empty tag in name for %s", id, key)
+				continue
+			}
+			tag = fmt.Sprintf("%s-%s", tag, t)
 		}
 		if tag[0:1] == "-" {
 			tag = tag[1:]

main_test.go

@@ -34,7 +34,10 @@ func TestBuild(t *testing.T) {
 		}
 	})
 
-	want := `build busybox -t localhost:5000/images/busybox:latest -t localhost:5000/images/busybox:7
+	want := `
+build alpine --build-arg MESSAGE=multiply -t localhost:5000/images/alpine:multiply -t localhost:5000/images/alpine:multiply-7
+build alpine --build-arg MESSAGE= -t localhost:5000/images/alpine:latest -t localhost:5000/images/alpine:7
+build busybox -t localhost:5000/images/busybox:latest -t localhost:5000/images/busybox:7
 build php --build-arg VERSION=7.2 --build-arg OS=alpine --build-arg NAME=test -t docker.io/bitsbeats/image1:7.2-alpine-test -t docker.io/bitsbeats/image1:7.2-alpine-test-7 -t docker.io/bitsbeats/image2:7.2-alpine-test -t docker.io/bitsbeats/image2:7.2-alpine-test-7 -t localhost:5000/images/php:7.2-alpine-test -t localhost:5000/images/php:7.2-alpine-test-7
 build php --build-arg VERSION=7.2 --build-arg OS=debian --build-arg NAME=test -t docker.io/bitsbeats/image1:7.2-debian-test -t docker.io/bitsbeats/image1:7.2-debian-test-7 -t docker.io/bitsbeats/image2:7.2-debian-test -t docker.io/bitsbeats/image2:7.2-debian-test-7 -t localhost:5000/images/php:7.2-debian-test -t localhost:5000/images/php:7.2-debian-test-7
 build php --build-arg VERSION=7.3 --build-arg OS=alpine --build-arg NAME=test -t docker.io/bitsbeats/image1:7.3-alpine-test -t docker.io/bitsbeats/image1:7.3-alpine-test-7 -t docker.io/bitsbeats/image2:7.3-alpine-test -t docker.io/bitsbeats/image2:7.3-alpine-test-7 -t localhost:5000/images/php:7.3-alpine-test -t localhost:5000/images/php:7.3-alpine-test-7
@@ -59,8 +62,12 @@ push docker.io/bitsbeats/image2:7.3-alpine-test
 push docker.io/bitsbeats/image2:7.3-alpine-test-7
 push docker.io/bitsbeats/image2:7.3-debian-test
 push docker.io/bitsbeats/image2:7.3-debian-test-7
-push localhost:5000/images/busybox:latest
+push localhost:5000/images/alpine:7
+push localhost:5000/images/alpine:latest
+push localhost:5000/images/alpine:multiply
+push localhost:5000/images/alpine:multiply-7
 push localhost:5000/images/busybox:7
+push localhost:5000/images/busybox:latest
 push localhost:5000/images/php:7.2-alpine-test
 push localhost:5000/images/php:7.2-alpine-test-7
 push localhost:5000/images/php:7.2-debian-test
@@ -78,6 +85,7 @@ push localhost:5000/images/python:3.6-alpine-7
 push localhost:5000/images/python:3.6-stretch
 push localhost:5000/images/python:3.6-stretch-7
 `
+	want = want [1:]
 
 	wantList := strings.Split(want, "\n")
 	gotList := strings.Split(got, "\n")

testdata/alpine/Dockerfile

@@ -0,0 +1,3 @@
+FROM alpine
+ARG MESSAGE="World"
+RUN echo Hello ${MESSAGE:-default}

testdata/alpine/docker-matrix.yml

@@ -0,0 +1,4 @@
+multiply:
+  MESSAGE:
+    - multiply
+    - ""