exec plugin: allow using glob pattern in command list

Allow using glob pattern in the command list in configuration. This enables for
example placing all commands in a single directory and using /path/to/dir/*.sh
as one of the commands to run all shell scripts in that directory.

Glob patterns are applied on every run of the commands, so matching commands can
be added without restarting telegraf.

plugins/inputs/exec/exec.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 	"os/exec"
+	"path/filepath"
 	"sync"
 	"syscall"
 
@@ -139,10 +140,19 @@ func (e *Exec) Gather(acc telegraf.Accumulator) error {
 		e.Command = ""
 	}
 
-	e.errChan = make(chan error, len(e.Commands))
+	commands := make([]string, len(e.Commands))
+	for _, pattern := range e.Commands {
+		matches, err := filepath.Glob(pattern)
+		if err != nil {
+			return err
+		}
+		commands = append(commands, matches...)
+	}
 
-	e.wg.Add(len(e.Commands))
+	e.errChan = make(chan error, len(commands))
-	for _, command := range e.Commands {
+
+	e.wg.Add(len(commands))
+	for _, command := range commands {
 		go e.ProcessCommand(command, acc)
 	}
 	e.wg.Wait()