diff --git a/docs/config_interpolation.md b/docs/config_interpolation.md
index 4498e7ca7b..090d5ec1bf 100644
--- a/docs/config_interpolation.md
+++ b/docs/config_interpolation.md
@@ -82,6 +82,9 @@ referred to will depend on the context of where the function is called.
 If a message contains the metadata key/value pair `foo: bar` the function
 `${!metadata:foo}` would resolve to `bar`.
 
+If the argument is ommited then all key/value pairs within the metadata will be
+printed in the following comma-separated format: `key1:value1,key2:value2,...`.
+
 Message metadata can be modified using the
 [metadata processor](./processors/README.md#metadata).
 
diff --git a/lib/util/text/function_vars.go b/lib/util/text/function_vars.go
index 4459587fd1..56642dafe7 100644
--- a/lib/util/text/function_vars.go
+++ b/lib/util/text/function_vars.go
@@ -24,6 +24,7 @@ import (
 	"bytes"
 	"os"
 	"regexp"
+	"sort"
 	"strconv"
 	"strings"
 	"sync"
@@ -40,6 +41,7 @@ type Message interface {
 	Get(p int) []byte
 	GetJSON(p int) (interface{}, error)
 	GetMetadata(key string) string
+	IterMetadata(func(k, v string) error) error
 	Len() int
 }
 
@@ -134,6 +136,19 @@ var functionVars = map[string]func(msg Message, arg string) []byte{
 	},
 	"json_field": jsonFieldFunction,
 	"metadata": func(m Message, arg string) []byte {
+		if len(arg) == 0 {
+			keys := []string{}
+			m.IterMetadata(func(k, _ string) error {
+				keys = append(keys, k)
+				return nil
+			})
+			sort.Strings(keys)
+			kvs := []string{}
+			for _, k := range keys {
+				kvs = append(kvs, k+":"+m.GetMetadata(k))
+			}
+			return []byte(strings.Join(kvs, ","))
+		}
 		return []byte(m.GetMetadata(arg))
 	},
 }
diff --git a/lib/util/text/function_vars_test.go b/lib/util/text/function_vars_test.go
index e1995c0aae..deb9d44dea 100644
--- a/lib/util/text/function_vars_test.go
+++ b/lib/util/text/function_vars_test.go
@@ -55,6 +55,7 @@ func TestFunctionVarDetection(t *testing.T) {
 func TestMetadataFunction(t *testing.T) {
 	msg := types.NewMessage(nil)
 	msg.SetMetadata("foo", "bar")
+	msg.SetMetadata("baz", "qux")
 
 	act := string(ReplaceFunctionVariables(
 		msg, []byte(`foo ${!metadata:foo} baz`),
@@ -69,6 +70,13 @@ func TestMetadataFunction(t *testing.T) {
 	if exp := "foo  baz"; act != exp {
 		t.Errorf("Wrong result: %v != %v", act, exp)
 	}
+
+	act = string(ReplaceFunctionVariables(
+		msg, []byte(`${!metadata}`),
+	))
+	if exp := "baz:qux,foo:bar"; act != exp {
+		t.Errorf("Wrong result: %v != %v", act, exp)
+	}
 }
 
 func TestJSONFunction(t *testing.T) {