Go语言圣经-入门
Go语言圣经-入门
命令行参数
os 包以跨平台的方式，提供了一些与操作系统交互的函数和变量。程序的命令行参数可从 os 包的 Args 变量获取；os 包外部使用 os.Args 访问该变量。
os.Args 的第一个元素：os.Args[0]，是命令本身的名字；其它的元素则是程序启动时传给它的参数。
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)
}> go run main.go 4 2 5 4 1
4 2 5 4 1for 循环的另一种形式，在某种数据类型的区间（range）上遍历
func main() {
var s, sep string
for _, j := range os.Args[1:] {
s += sep + j
sep = " "
}
fmt.Println(s)
}使用 strings 包的 Join 函数：
func main() {
fmt.Println(strings.Join(os.Args[1:], " "))
}查找重复的行
// Dup1 prints the text of each line that appears more than
// once in the standard input, preceded 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: ignoring potential errors from input.Err()
for line, n := range counts {
if n > 1 {
fmt.Printf("%d\t%s\n", n, line)
}
}
}
> abc
> abc
> def
> efd
> efd
2 abc
2 efdPrintf的多种转换形式：
%d 十进制整数
%x, %o, %b 十六进制，八进制，二进制整数。
%f, %g, %e 浮点数： 3.141593 3.141592653589793 3.141593e+00
%t 布尔：true或false
%c 字符（rune） (Unicode码点)
%s 字符串
%q 带双引号的字符串"abc"或带单引号的字符'c'
%v 变量的自然形式（natural format）
%T 变量的类型
%% 字面上的百分号标志（无操作数）以 ln 结尾的格式化函数，则遵循 Println 的方式，以跟 %v 差不多的方式格式化参数，并在最后添加一个换行符。
第二个版本，可以接收文件并判断重复行
// Dup2 prints the count and text of lines that appear more than once
// in the input. It reads from 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 _, 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()
}
}
for line, n := range counts {
if n > 1 {
fmt.Printf("%d\t%s\n", n, line)
}
}
}
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()
}
map 是一个由 make 函数创建的数据结构的引用。map 作为参数传递给某函数时，该函数接收这个引用的一份拷贝（copy，或译为副本），被调用函数对 map 底层数据结构的任何修改，调用者函数都可以通过持有的 map 引用看到。
package main
import (
"fmt"
"os"
"strings"
)
func main() {
counts := make(map[string]int)
for _, filename := range os.Args[1:] {
data, err := os.ReadFile(filename)
if err != nil {
fmt.Fprintf(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)
}
}
}
引入了 ReadFile 函数（来自于 os包），其读取指定文件的全部内容，strings.Split 函数把字符串分割成子串的切片。
GIF动画
// Lissajous generates GIF animations of random Lissajous figures.
package main
import (
"image"
"image/color"
"image/gif"
"io"
"math"
"math/rand"
"os"
"time"
)
var palette = []color.Color{color.White, color.Black}
const (
whiteIndex = 0 // first color in palette
blackIndex = 1 // next color in palette
)
func main() {
// The sequence of images is deterministic unless we seed
// the pseudo-random number generator using the current time.
// Thanks to Randall McPherson for pointing out the omission.
rand.Seed(time.Now().UTC().UnixNano())
lissajous(os.Stdout)
}
func lissajous(out io.Writer) {
const (
cycles = 5 // number of complete x oscillator revolutions
res = 0.001 // angular resolution
size = 100 // image canvas covers [-size..+size]
nframes = 64 // number of animation frames
delay = 8 // delay between frames in 10ms units
)
freq := rand.Float64() * 3.0 // relative frequency of y oscillator
anim := gif.GIF{LoopCount: nframes}
phase := 0.0 // phase difference
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) // NOTE: ignoring encoding errors
}
获取URL
// Fetch prints the content found at a URL.
package main
import (
"fmt"
"io"
"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 := io.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)
}
}
改进：
避免申请缓冲区、url参数没有 http:// 前缀、打印出HTTP协议的状态码
// Fetch prints the content found at a URL.
package main
import (
"fmt"
"io"
"net/http"
"os"
"strings"
)
func main() {
for _, url := range os.Args[1:] {
if !strings.HasPrefix(url, "http://") {
url = "http://" + url
}
resp, err := http.Get(url)
if err != nil {
fmt.Fprintf(os.Stderr, "fetch: %v\n", err)
os.Exit(1)
}
_, err = io.Copy(os.Stdout, resp.Body)
if err != nil {
fmt.Fprintf(os.Stderr, "fetch: reading %s: %v\n", url, err)
os.Exit(1)
}
fmt.Println(resp.Status)
resp.Body.Close()
}
}
并发获取多个URL
// Fetchall fetches URLs in parallel and reports their times and sizes.
package main
import (
"fmt"
"io"
"net/http"
"os"
"time"
)
func main() {
start := time.Now()
ch := make(chan string)
for _, url := range os.Args[1:] {
go fetch(url, ch) // start a goroutine
}
for range os.Args[1:] {
fmt.Println(<-ch) // receive from channel ch
}
fmt.Printf("%.2fs elapsed\n", time.Since(start).Seconds())
}
func fetch(url string, ch chan<- string) {
start := time.Now()
resp, err := http.Get(url)
if err != nil {
ch <- fmt.Sprint(err) // send to channel ch
return
}
nbytes, err := io.Copy(io.Discard, resp.Body)
resp.Body.Close() // don't leak resources
if err != nil {
ch <- fmt.Sprintf("while reading %s: %v", url, err)
return
}
secs := time.Since(start).Seconds()
ch <- fmt.Sprintf("%.2fs %7d %s", secs, nbytes, url)
}
goroutine是一种函数的并发执行方式，而channel是用来在goroutine之间进行参数传递。main函数本身也运行在一个goroutine中，而go function则表示创建一个新的goroutine，并在这个新的goroutine中执行这个函数。
Web服务
// Server1 is a minimal "echo" server.
package main
import (
"fmt"
"log"
"net/http"
)
func main() {
http.HandleFunc("/", handler) // each request calls handler
log.Fatal(http.ListenAndServe("localhost:8000", nil))
}
// handler echoes the Path component of the request URL r.
func handler(w http.ResponseWriter, r *http.Request) {
fmt.Fprintf(w, "URL.Path = %q\n", r.URL.Path)
}为访问的url添加某种状态。比如，下面这个版本输出了同样的内容，但是会对请求的次数进行计算
// Server2 is a minimal "echo" and counter server.
package main
import (
"fmt"
"log"
"net/http"
"sync"
)
var mu sync.Mutex
var count int
func main() {
http.HandleFunc("/", handler)
http.HandleFunc("/count", counter)
log.Fatal(http.ListenAndServe("localhost:8000", nil))
}
// handler echoes the Path component of the requested URL.
func handler(w http.ResponseWriter, r *http.Request) {
mu.Lock()
count++
mu.Unlock()
fmt.Fprintf(w, "URL.Path = %q\n", r.URL.Path)
}
// counter echoes the number of calls so far.
func counter(w http.ResponseWriter, r *http.Request) {
mu.Lock()
fmt.Fprintf(w, "Count %d\n", count)
mu.Unlock()
}
handler函数会把请求的http头和请求的form数据都打印出来，这样可以使检查和调试这个服务更为方便
// handler echoes the HTTP request.
func handler(w http.ResponseWriter, r *http.Request) {
fmt.Fprintf(w, "%s %s %s\n", r.Method, r.URL, r.Proto)
for k, v := range r.Header {
fmt.Fprintf(w, "Header[%q] = %q\n", k, v)
}
fmt.Fprintf(w, "Host = %q\n", r.Host)
fmt.Fprintf(w, "RemoteAddr = %q\n", r.RemoteAddr)
if err := r.ParseForm(); err != nil {
log.Print(err)
}
for k, v := range r.Form {
fmt.Fprintf(w, "Form[%q] = %q\n", k, v)
}
}Go语言圣经-入门
https://zhangzhao219.github.io/2022/10/09/Go/go-basic-1/