Allow nested interpolation

Author: matteosuppo

exec/exec.go

@@ -54,8 +54,12 @@ import (
 
 // Interpolate substitutes the params with the corresponding options
 func Interpolate(pattern string, opts map[string]string) (interpolated []string, err error) {
-	for key, value := range opts {
-		pattern = strings.Replace(pattern, "{"+key+"}", value, -1)
+	oldPattern := ""
+	for pattern != oldPattern {
+		oldPattern = pattern
+		for key, value := range opts {
+			pattern = strings.Replace(pattern, "{"+key+"}", value, -1)
+		}
 	}
 
 	z, err := shellwords.Parse(pattern)

exec/exec_test.go

@@ -87,6 +87,18 @@ func TestLocal(t *testing.T) {
 			"",
 			nil,
 		},
+		{
+			"nested interpolation",
+			"echo {interpolate.string}",
+			map[string]string{
+				"greeting":           "hello",
+				"target":             "world",
+				"interpolate.string": "{greeting} {target}",
+			},
+			"hello world",
+			"",
+			nil,
+		},
 		{
 			"inject ; to perform other commands has no effect",
 			"echo {interpolate.string}",