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 #1142

plugins/inputs/exec/exec.go

@@ -4,6 +4,8 @@ import (
 	"bytes"
 	"fmt"
 	"os/exec"
+	"path/filepath"
+	"strings"
 	"sync"
 	"syscall"
 	"time"
@@ -19,7 +21,11 @@ import (
 
 const sampleConfig = `
   ## Commands array
-  commands = ["/tmp/test.sh", "/usr/bin/mycollector --foo=bar"]
+  commands = [
+    "/tmp/test.sh",
+    "/usr/bin/mycollector --foo=bar",
+    "/tmp/collect_*.sh"
+  ]
 
   ## Timeout for each command to complete.
   timeout = "5s"
@@ -150,10 +156,36 @@ func (e *Exec) Gather(acc telegraf.Accumulator) error {
 		e.Command = ""
 	}
 
-	e.errChan = make(chan error, len(e.Commands))
+	commands := make([]string, 0, len(e.Commands))
+	for _, pattern := range e.Commands {
+		cmdAndArgs := strings.SplitN(pattern, " ", 2)
+		if len(cmdAndArgs) == 0 {
+			continue
+		}
 
-	e.wg.Add(len(e.Commands))
-	for _, command := range e.Commands {
+		matches, err := filepath.Glob(cmdAndArgs[0])
+		if err != nil {
+			return err
+		}
+
+		if len(matches) == 0 {
+			// There were no matches with the glob pattern, so let's assume
+			// that the command is in PATH and just run it as it is
+			commands = append(commands, pattern)
+		} else {
+			// There were matches, so we'll append each match together with
+			// the arguments to the commands slice
+			for _, match := range matches {
+				commands = append(
+					commands, strings.Join([]string{match, cmdAndArgs[1]}, " "))
+			}
+		}
+	}
+
+	e.errChan = make(chan error, len(commands))
+
+	e.wg.Add(len(commands))
+	for _, command := range commands {
 		go e.ProcessCommand(command, acc)
 	}
 	e.wg.Wait()