init

dup3/hello

@@ -0,0 +1,11 @@
+hello
+hello
+hello
+hello
+world
+world
+world
+world
+world
+hello
+hello

dup3/main.go

@@ -0,0 +1,27 @@
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"strings"
+)
+
+func main() {
+	counts := make(map[string]int)
+	for _, filname := range os.Args[1:] {
+		data, err := ioutil.ReadFile(filname)
+		if err != nil {
+			fmt.Fprint(os.Stderr, "dup3: %v\n", err)
+			continue
+		}
+		for _, line := range strings.Split(string(data), "\n") {
+			counts[line]++
+		}
+	}
+	for line, n := range counts {
+		if n > 1 {
+			fmt.Printf("%d\t%s\n", n, line)
+		}
+	}
+}