Adding support to getenv for a default value

Fixes #14

Signed-off-by: Dave Henderson <dhenderson@gmail.com>

main.go

@@ -25,9 +25,15 @@ func init() {
 }
 
 // Getenv retrieves the value of the environment variable named by the key.
-// It returns the value, which will be empty if the variable is not present.
-func Getenv(key string) string {
-	return os.Getenv(key)
+// It returns the value, or the default (or an emptry string) if the variable is
+// not set.
+func Getenv(key string, def ...string) string {
+	val := os.Getenv(key)
+	if val == "" && len(def) > 0{
+		return def[0]
+	} else {
+		return os.Getenv(key)
+	}
 }
 
 // Bool converts a string to a boolean value, using strconv.ParseBool under the covers.

main_test.go

@@ -21,6 +21,7 @@ func TestGetenv(t *testing.T) {
 	assert.Empty(t, testTemplate(`{{getenv "BLAHBLAHBLAH"}}`))
 	assert.Equal(t, Getenv("USER"), os.Getenv("USER"))
 	assert.Equal(t, os.Getenv("USER"), testTemplate(`{{getenv "USER"}}`))
+	assert.Equal(t, "default value", testTemplate(`{{getenv "BLAHBLAHBLAH" "default value"}}`))
 }
 
 func TestBool(t *testing.T) {