Implemented basic useprog command.

src/cmd/goblin/main.go

@@ -24,6 +24,7 @@ import(
 	"github.com/surdeus/goblin/src/tool/ftest"
 	"github.com/surdeus/goblin/src/tool/grange"
 	"github.com/surdeus/goblin/src/tool/in"
+	"github.com/surdeus/goblin/src/tool/useprog"
 )
 
 func main() {
@@ -50,6 +51,7 @@ func main() {
 		"ftest" : mtool.Tool{ftest.Run, "filter files by specified features"},
 		"range" : mtool.Tool{grange.Run, "too lazy"},
 		"in" : mtool.Tool{in.Run, "filter strings from stdin that aren not in arguments"},
+		"useprog" : mtool.Tool{useprog.Run, "print the name of the first existing program in arg list"},
 	}
 
 	mtool.Main("goblin", tools)

src/tool/useprog/main.go

@@ -0,0 +1,35 @@
+package useprog
+
+import (
+	"os"
+	"os/exec"
+	"fmt"
+	"flag"
+)
+
+func Run(args []string) {
+	arg0 := args[0]
+	args = args[1:]
+	flagSet := flag.NewFlagSet(arg0, flag.ExitOnError)
+	flagSet.Usage = func() {
+		fmt.Fprintf(os.Stderr, "usage: %s <prog1> [prog2, ...prog3]\n", arg0)
+		flagSet.PrintDefaults()
+		os.Exit(1)
+	}
+
+	flagSet.Parse(args)
+	args = flagSet.Args()
+
+	if len(args) == 0 {
+		flagSet.Usage()
+	}
+
+	for _, v := range args {
+		_, err := exec.LookPath(v)
+		if err != nil {
+			continue
+		}
+		fmt.Printf("%s", v)
+		break
+	}
+}