init

#echo1.go#

@@ -0,0 +1,16 @@
+// Echo1 prints its command-line arguments.
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func main() {
+	var s, sep string
+	for i := 1;i < len(os.Args); i++ {
+		s += sep + os.Args[i]
+		sep = " "
+	}
+	fmt.Println(s)
+}

.envrc

@@ -0,0 +1 @@
+use nix 

default.nix

@@ -0,0 +1,9 @@
+{ pkgs ? import <nixpkgs> {}}:
+
+pkgs.mkShell {
+  packages = [
+    pkgs.go
+    pkgs.gopls
+    pkgs.gotools
+  ];
+}

default.nix~

@@ -0,0 +1,8 @@
+{ pkgs ? import <nixpkgs> {}}:
+
+pkgs.mkShell {
+  packages = [
+    pkgs.go
+    pkgs.gopls
+  ];
+}

dup/dup1.go

@@ -0,0 +1,26 @@
+// Dup1 prints the text of each line that appears more than
+// once in the standard input, preceeded by its count.
+
+package main
+
+import(
+	"bufio"
+	"fmt"
+	"os"
+)
+
+func main() {
+	counts := make(map[string]int)
+	input := bufio.NewScanner(os.Stdin)
+
+	for input.Scan() {
+		counts[input.Text()]++
+	}
+	//NOTE: ingnoring potential errors from input.Err()
+	for line, n := range counts {
+		if n > 1 {
+			fmt.Printf("%d\t%s\n", n , line)
+		}
+	}
+	
+}

dup2/dup2.go

@@ -0,0 +1,33 @@
+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 _, arg := range files {
+			f, err := os.Open(arg)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "dup2: %v\n", err)
+				continue
+			}
+			countLines(f, counts)
+			f.Close()
+		}
+	}
+	
+}
+
+func countLines(f *os.File, counts map[string]int) {
+	input := bufio.NewScanner(f)
+	for input.Scan() {
+		counts[input.Text()]++
+	}
+}

dup2/test.txt

@@ -0,0 +1,4 @@
+test
+test
+test
+test

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)
+		}
+	}
+}

echov1/echo1.go

@@ -0,0 +1,16 @@
+//Echo1 prints its command-line arguments.
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func main() {
+	var s, sep string
+	for i := 1;i < len(os.Args); i++ {
+		s += sep + os.Args[i]
+		sep = " "
+	}
+	fmt.Println(s)
+}

echov2/echo.go

@@ -0,0 +1,19 @@
+// Echov2 prints its command-line arguments.
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func main() {
+	s, sep := "", ""
+	for _, arg := range os.Args[1:] {
+		s += sep + arg
+		sep = " "
+	}
+	fmt.Println(s)
+	for i, v := range os.Args[1:] {
+		println(i,v)
+	}
+}

echov3/echo.go

@@ -0,0 +1,13 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+func main() {
+	fmt.Println(strings.Join(os.Args[1:], " "))
+	fmt.Print(os.Args[0:])
+	
+}

fetch/main.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"os"
+)
+
+func main() {
+	for _, url := range os.Args[1:] {
+		resp, err := http.Get(url)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "fetch: %v\n", err)
+			os.Exit(1)
+		}
+		b, err := ioutil.ReadAll(resp.Body)
+		resp.Body.Close()
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "fetch: reading %s: %v\n", url, err)
+			os.Exit(1)
+		}
+		fmt.Printf("%s", b)
+	}
+}

hello/helloworld.go

@@ -0,0 +1,7 @@
+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println("hello 世界")
+}

helloworld.go~

@@ -0,0 +1,7 @@
+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println("hello world")
+}

lisajous/lisajous.go

@@ -0,0 +1,49 @@
+// Lisajous generates GIF animations of random Lisajous figures.
+package main
+
+import (
+	"image"
+	"image/color"
+	"image/gif"
+	"io"
+	"math"
+	"math/rand"
+	"os"
+)
+
+var palette = [] color.Color{color.White, color.Black}
+
+const (
+	whiteIndex = 0
+	blackindex = 1
+)
+
+func main() {
+	lisajous(os.Stdout)
+}
+
+func lisajous(out io.Writer) {
+	const (
+		cycles = 5
+		res = 0.001
+		size = 100
+		nframes = 64
+		delay = 8
+	)
+	freq := rand.Float64() * 3.0
+	anim := gif.GIF{LoopCount: nframes}
+	phase := 0.0
+	for i := 0; i < nframes; i++ {
+		rect := image.Rect(0, 0, 2*size+1, 2*size+1)
+		img := image.NewPaletted(rect, palette)
+		for t := 0.0; t < cycles*2*math.Pi; t += res {
+			x := math.Sin(t)
+			y := math.Sin(t*freq + phase)
+			img.SetColorIndex(size+int(x*size+0.5), size+int(y*size+0.5), blackindex)
+		}
+		phase += 0.1
+		anim.Delay = append(anim.Delay, delay)
+		anim.Image = append(anim.Image, img)
+	}
+	gif.EncodeAll(out, &anim)
+}