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.

closes #1127

plugins/inputs/exec/exec.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 	"os/exec"
+	"path/filepath"
 	"sync"
 	"syscall"
 	"time"
@@ -18,8 +19,11 @@ import (
 )
 
 const sampleConfig = `
-  ## Commands array
-  commands = ["/tmp/test.sh", "/usr/bin/mycollector --foo=bar"]
+  ## Full path to executable with parameters,
+  ## or a glob pattern to run all matching files.
+  ## the glob pattern will be run at every interval, so new files will
+  ## automatically be picked up.
+  commands = ["/tmp/test.sh", "/usr/bin/collector --foo=bar", "/tmp/collect_*.sh"]
 
   ## Timeout for each command to complete.
   timeout = "5s"
@@ -150,10 +154,19 @@ 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))
-	for _, command := range e.Commands {
+	e.errChan = make(chan error, len(commands))
+
+	e.wg.Add(len(commands))
+	for _, command := range commands {
 		go e.ProcessCommand(command, acc)
 	}
 	e.wg.Wait()