...

ch1/exercise1.3/main.go

@@ -0,0 +1,32 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+func main() {
+}
+
+func echo1(args []string) {
+	var s, sep string
+
+	for i := 0; i < len(args); i++ {
+		s += sep + args[i]
+		sep = " "
+	}
+	fmt.Println(s)
+}
+
+func echo2(args []string) {
+	s, sep := "", ""
+	for _, arg := range args[1:] {
+		s += sep + arg
+		sep = " "
+	}
+	fmt.Println(s)
+}
+
+func echo3(args []string) {
+	fmt.Println(strings.Join(args[1:], " "))
+}

ch1/exercise1.4/main.go

@@ -0,0 +1,50 @@
+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+// Dup2 prints the count and text of lines that appears more than once in the input
+// It reads form stdin or from a list of named files.
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+)
+
+func main() {
+	counts := make(map[string]int)
+	files := os.Args[1:]
+	if len(files) == 0 {
+		countLines(os.Stdin, counts)
+	} else {
+		for i, arg := range files {
+			f, err := os.Open(arg)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "dup2: %v\n", err)
+				continue
+			}
+			fmt.Println("Filename:", files[i])
+			countLines(f, counts)
+			f.Close()
+		}
+	}
+	for line, n := range counts {
+		if n > 1 {
+			fmt.Printf("%d\t%s\n", n, line)
+		}
+	}
+}
+
+// NOTE:
+// A map is a reference to the data structure created by make.
+// When a map is passed to a function, the function receives a copy of the reference,
+// so any changes the called function makes to the underlying data structure
+// will be visible through the caller ’s map reference too.
+// In our example, the values inserted into the counts map by countLines are seen by main.
+func countLines(f *os.File, counts map[string]int) {
+	input := bufio.NewScanner(f)
+	for input.Scan() {
+		counts[input.Text()]++
+	}
+	// NOTE: ignoring potential errors from input.err
+}