diff --git a/ch1/ex1.4/main.go b/ch1/ex1.4/main.go
new file mode 100644
index 0000000..4920b87
--- /dev/null
+++ b/ch1/ex1.4/main.go
@@ -0,0 +1,51 @@
+// ex1.4 solves exercise 1.4
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+)
+
+func main() {
+	counts := make(map[string]int)
+	files := make(map[string]map[string]bool)
+	inputs := os.Args[1:]
+	if len(inputs) == 0 {
+		countLines(os.Stdin, counts, files)
+	} else {
+		for _, arg := range inputs {
+			f, err := os.Open(arg)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "ex1.4: %v\n", err)
+				continue
+			}
+			if err := countLines(f, counts, files); err != nil {
+				panic(err)
+			}
+			f.Close()
+		}
+	}
+	for line, n := range counts {
+		if n > 1 {
+			fmt.Printf("%d\t%q\n", n, line)
+			for file := range files[line] {
+				fmt.Printf("\tin %q\n", file)
+			}
+		}
+	}
+}
+
+func countLines(f *os.File, counts map[string]int, files map[string]map[string]bool) error {
+	input := bufio.NewScanner(f)
+	for input.Scan() {
+		line := input.Text()
+		counts[line]++
+
+		if _, ok := files[line]; !ok {
+			files[line] = make(map[string]bool)
+		}
+		files[line][f.Name()] = true
+	}
+	return input.Err()
+}