Added a 'split' function to parse template variables.

packer/test-fixtures/build-split-func.json

@@ -0,0 +1,6 @@
+{
+    "builders": [{
+        "type": "test",
+        "value": "{{split \"foo-bar\" \"-\" 0}}"
+    }]
+}

template/interpolate/funcs.go

@@ -30,6 +30,7 @@ var FuncGens = map[string]FuncGenerator{
 	"env":            funcGenEnv,
 	"isotime":        funcGenIsotime,
 	"pwd":            funcGenPwd,
+	"split":          funcGenSplitter,
 	"template_dir":   funcGenTemplateDir,
 	"timestamp":      funcGenTimestamp,
 	"uuid":           funcGenUuid,
@@ -60,6 +61,17 @@ func Funcs(ctx *Context) template.FuncMap {
 	return template.FuncMap(result)
 }
 
+func funcGenSplitter(ctx *Context) interface{} {
+	return func(k string, s string, i int) (string, error) {
+		// return func(s string) (string, error) {
+		split := strings.Split(k, s)
+		if len(split) <= i {
+			return "", fmt.Errorf("the substring %d was unavailable using the separator value, %s, only %d values were found", i, s, len(split))
+		}
+		return split[i], nil
+	}
+}
+
 func funcGenBuildName(ctx *Context) interface{} {
 	return func() (string, error) {
 		if ctx == nil || ctx.BuildName == "" {

template/interpolate/funcs_test.go

@@ -200,6 +200,31 @@ func TestFuncTemplatePath(t *testing.T) {
 	}
 }
 
+func TestFuncSplit(t *testing.T) {
+	cases := []struct {
+		Input  string
+		Output string
+	}{
+		{
+			`{{split build_name "-" 0}}`,
+			"foo",
+		},
+	}
+
+	ctx := &Context{BuildName: "foo-bar"}
+	for _, tc := range cases {
+		i := &I{Value: tc.Input}
+		result, err := i.Render(ctx)
+		if err != nil {
+			t.Fatalf("Input: %s\n\nerr: %s", tc.Input, err)
+		}
+
+		if result != tc.Output {
+			t.Fatalf("Input: %s\n\nGot: %s", tc.Input, result)
+		}
+	}
+}
+
 func TestFuncTimestamp(t *testing.T) {
 	expected := strconv.FormatInt(InitTime.Unix(), 10)
 

website/source/docs/templates/engine.html.md

@@ -38,6 +38,7 @@ Here is a full list of the available functions for reference.
     examples below in [the `isotime` format reference](/docs/templates/engine.html#isotime-function-format-reference).
 -   `lower` - Lowercases the string.
 -   `pwd` - The working directory while executing Packer.
+-   `split` - Split an input string using separator and return the requested substring.
 -   `template_dir` - The directory to the template for the build.
 -   `timestamp` - The current Unix timestamp in UTC.
 -   `uuid` - Returns a random UUID.
@@ -225,3 +226,37 @@ Please note that double quote characters need escaping inside of templates (in t
 ```
 
 -> **Note:** See the [Amazon builder](/docs/builders/amazon.html) documentation for more information on how to correctly configure the Amazon builder in this example.
+
+# split Function Format Reference
+
+The function `split` takes an input string, a seperator string, and a numeric component value and returns request substring.
+
+Here are some examples using the above options:
+
+``` liquid
+build_name = foo-bar-provider
+
+{{split build_name "-" 0}} = foo
+{{split "fixed-string" "-" 1}} = string
+```
+
+Please note that double quote characters need escaping inside of templates (in this case, on the `fixed-string` value):
+
+``` json
+{
+  "post-processors": [
+    [
+      {
+        "type": "vagrant",
+        "compression_level": 9,
+        "keep_input_artifact": false,
+        "vagrantfile_template": "tpl/{{split build_name \"-\" 1}.rb",
+        "output": "output/{{build_name}}.box",
+        "only": [
+            "org-name-provider"
+        ]
+      }
+    ]
+  ]
+}
+```