Add support for ${} env vars in configuration file (#5648)

docs/CONFIGURATION.md

@@ -34,10 +34,10 @@ configuration files.
 
 ### Environment Variables
 
-Environment variables can be used anywhere in the config file, simply prepend
-them with `$`.  Replacement occurs before file parsing.   For strings
-the variable must be within quotes, e.g., `"$STR_VAR"`, for numbers and booleans
-they should be unquoted, e.g., `$INT_VAR`, `$BOOL_VAR`.
+Environment variables can be used anywhere in the config file, simply surround
+them with `${}`.  Replacement occurs before file parsing.   For strings
+the variable must be within quotes, e.g., `"${STR_VAR}"`, for numbers and booleans
+they should be unquoted, e.g., `${INT_VAR}`, `${BOOL_VAR}`.
 
 When using the `.deb` or `.rpm` packages, you can define environment variables
 in the `/etc/default/telegraf` file.
@@ -55,14 +55,14 @@ INFLUX_PASSWORD="monkey123"
 `/etc/telegraf.conf`:
 ```toml
 [global_tags]
-  user = "$USER"
+  user = "${USER}"
 
 [[inputs.mem]]
 
 [[outputs.influxdb]]
-  urls = ["$INFLUX_URL"]
-  skip_database_creation = $INFLUX_SKIP_DATABASE_CREATION
-  password = "$INFLUX_PASSWORD"
+  urls = ["${INFLUX_URL}"]
+  skip_database_creation = ${INFLUX_SKIP_DATABASE_CREATION}
+  password = "${INFLUX_PASSWORD}"
 ```
 
 The above files will produce the following effective configuration file to be

internal/config/config.go

@@ -40,7 +40,7 @@ var (
 	outputDefaults = []string{"influxdb"}
 
 	// envVarRe is a regex to find environment variables in the config file
-	envVarRe = regexp.MustCompile(`\$\w+`)
+	envVarRe = regexp.MustCompile(`\$\{(\w+)\}|\$(\w+)`)
 
 	envVarEscaper = strings.NewReplacer(
 		`"`, `\"`,
@@ -208,9 +208,9 @@ var header = `# Telegraf Configuration
 # Use 'telegraf -config telegraf.conf -test' to see what metrics a config
 # file would generate.
 #
-# Environment variables can be used anywhere in this config file, simply prepend
-# them with $. For strings the variable must be within quotes (ie, "$STR_VAR"),
-# for numbers and booleans they should be plain (ie, $INT_VAR, $BOOL_VAR)
+# Environment variables can be used anywhere in this config file, simply surround
+# them with ${}. For strings the variable must be within quotes (ie, "${STR_VAR}"),
+# for numbers and booleans they should be plain (ie, ${INT_VAR}, ${BOOL_VAR})
 
 
 # Global tags can be specified here in key="value" format.
@@ -787,12 +787,25 @@ func fetchConfig(u *url.URL) ([]byte, error) {
 func parseConfig(contents []byte) (*ast.Table, error) {
 	contents = trimBOM(contents)
 
-	env_vars := envVarRe.FindAll(contents, -1)
-	for _, env_var := range env_vars {
+	parameters := envVarRe.FindAllSubmatch(contents, -1)
+	for _, parameter := range parameters {
+		if len(parameter) != 3 {
+			continue
+		}
+
+		var env_var []byte
+		if parameter[1] != nil {
+			env_var = parameter[1]
+		} else if parameter[2] != nil {
+			env_var = parameter[2]
+		} else {
+			continue
+		}
+
 		env_val, ok := os.LookupEnv(strings.TrimPrefix(string(env_var), "$"))
 		if ok {
 			env_val = escapeEnv(env_val)
-			contents = bytes.Replace(contents, env_var, []byte(env_val), 1)
+			contents = bytes.Replace(contents, parameter[0], []byte(env_val), 1)
 		}
 	}
 

internal/config/config_test.go

@@ -11,7 +11,6 @@ import (
 	"github.com/influxdata/telegraf/plugins/inputs/memcached"
 	"github.com/influxdata/telegraf/plugins/inputs/procstat"
 	"github.com/influxdata/telegraf/plugins/parsers"
-
 	"github.com/stretchr/testify/assert"
 )
 
@@ -28,7 +27,7 @@ func TestConfig_LoadSingleInputWithEnvVars(t *testing.T) {
 
 	filter := models.Filter{
 		NameDrop:  []string{"metricname2"},
-		NamePass:  []string{"metricname1"},
+		NamePass:  []string{"metricname1", "ip_192.168.1.1_name"},
 		FieldDrop: []string{"other", "stuff"},
 		FieldPass: []string{"some", "strings"},
 		TagDrop: []models.TagFilter{

internal/config/testdata/single_plugin_env_vars.toml

@@ -1,6 +1,6 @@
 [[inputs.memcached]]
   servers = ["$MY_TEST_SERVER"]
-  namepass = ["metricname1"]
+  namepass = ["metricname1", "ip_${MY_TEST_SERVER}_name"]
   namedrop = ["metricname2"]
   fieldpass = ["some", "strings"]
   fielddrop = ["other", "stuff"]