From d3af8fd873caa7d982df30df727b5540312bc222 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adri=C3=A1n=20L=C3=B3pez?= <adrianlzt@gmail.com>
Date: Sat, 15 Jun 2019 00:23:54 +0200
Subject: [PATCH] Allow regexp processor to mix different tags (#5863)

---
 plugins/processors/regex/README.md     |  2 ++
 plugins/processors/regex/regex.go      |  6 ++++++
 plugins/processors/regex/regex_test.go | 14 ++++++++++++++
 3 files changed, 22 insertions(+)

diff --git a/plugins/processors/regex/README.md b/plugins/processors/regex/README.md
index d37b1ea88..a6cef82a0 100644
--- a/plugins/processors/regex/README.md
+++ b/plugins/processors/regex/README.md
@@ -2,6 +2,8 @@
 
 The `regex` plugin transforms tag and field values with regex pattern. If `result_key` parameter is present, it can produce new tags and fields from existing ones.
 
+For tags transforms, if `append` is set to `true`, it will append the transformation to the existing tag value, instead of overwriting it.
+
 ### Configuration:
 
 ```toml
diff --git a/plugins/processors/regex/regex.go b/plugins/processors/regex/regex.go
index b922cd2d5..47b53546f 100644
--- a/plugins/processors/regex/regex.go
+++ b/plugins/processors/regex/regex.go
@@ -18,6 +18,7 @@ type converter struct {
 	Pattern     string
 	Replacement string
 	ResultKey   string
+	Append      bool
 }
 
 const sampleConfig = `
@@ -70,6 +71,11 @@ func (r *Regex) Apply(in ...telegraf.Metric) []telegraf.Metric {
 		for _, converter := range r.Tags {
 			if value, ok := metric.GetTag(converter.Key); ok {
 				if key, newValue := r.convert(converter, value); newValue != "" {
+					if converter.Append {
+						if v, ok := metric.GetTag(key); ok {
+							newValue = v + newValue
+						}
+					}
 					metric.AddTag(key, newValue)
 				}
 			}
diff --git a/plugins/processors/regex/regex_test.go b/plugins/processors/regex/regex_test.go
index f16ef7f5c..b0ddf47d0 100644
--- a/plugins/processors/regex/regex_test.go
+++ b/plugins/processors/regex/regex_test.go
@@ -108,6 +108,20 @@ func TestTagConversions(t *testing.T) {
 				"resp_code": "2xx",
 			},
 		},
+		{
+			message: "Should append to existing tag",
+			converter: converter{
+				Key:         "verb",
+				Pattern:     "^(.*)$",
+				Replacement: " (${1})",
+				ResultKey:   "resp_code",
+				Append:      true,
+			},
+			expectedTags: map[string]string{
+				"verb":      "GET",
+				"resp_code": "200 (GET)",
+			},
+		},
 		{
 			message: "Should add new tag",
 			converter: converter{