Golang实践：HelloWorld
发布于 2017-08-29 · 本文总共 4110 字 · 阅读大约需要
12 分钟
hello， world
package main
import "fmt"
func main() {
fmt.Println("Hello, World!")
}
go run将一个或者多个以.go为后缀的源文件进行编译、链接，然后运行生成的可执行文件；
go run helloworld.go
% go run helloworld.go
Hello, World!
Go原生的支持Unicode，可以处理所有国家的语言；
package main
import "fmt"
func main() {
fmt.Println("Hello, World!")
fmt.Println("你好, 世界!")
}
go run:
% go run helloworld.go
Hello, World!
你好, 世界!
go build编译成可执行文件：
go build helloworld.go
./helloworld
Hello, World!
你好, 世界!
Printf函数转义字符
| verb | 描述 |
|---|---|
| %d | 十进制整数 |
| %x,%o,%b | 十六进制、八进制、二进制 |
| %f,%g,%e | 浮点数 |
| %t | 布尔类型 |
| %c | 字符 |
| %s | 字符串 |
| %q | 带引号字符串 |
| %v | 内置格式的任何值 |
| %T | 任何值的类型 |
| %% | 百分号 |
实践：命令行参数
package main
import (
"fmt"
"os"
)
func main() {
s := ""
seq := ""
for i := 1; i < len(os.Args); i++ {
s += seq + os.Args[i]
seq = " "
}
fmt.Println(s)
}
go run：
./command hello world
hello world
使用strings.Join：
package main
import (
"fmt"
"os"
"strings"
)
func main() {
fmt.Println(strings.Join(os.Args[1:], " "))
}
实践：找出重复行
模仿uniq命令，写一个程序找出输入的重复行：
$ cat test.txt
hello
hello
h
1
2
3
$ cat test.txt|uniq
hello
h
1
2
3
标准输入
dup：
package main
import (
"bufio"
"fmt"
"os"
)
func main() {
Dup()
}
func Dup() {
counts := make(map[string]int)
input := bufio.NewScanner(os.Stdin)
for input.Scan() {
counts[input.Text()]++
}
for line, n := range counts {
if n > 1 {
fmt.Printf("%d\t%s\n", n, line)
}
}
}
dup
go build dup.go
cat test.txt | ./dup
true hello
从文件读取
package main
import (
"bufio"
"fmt"
"os"
)
func main() {
DupLinesInFiles()
}
func DupLinesInFiles() {
counts := make(map[string]int)
files := os.Args[1:]
if len(files) == 0 {
return
} else {
for _, file := range files {
fp, err := os.Open(file)
if err != nil {
fmt.Fprintf(os.Stderr, "dup lines in file %s, error: %v\n", file, err)
continue
}
countLines(fp, counts)
fp.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()]++
}
}
cp test.txt test1.txt
./dup1 test.txt
2 hello
./dup1 test.txt test1.txt
2 2
2 3
4 hello
2 h
2 1
使用ioutil.ReadFile
package main
import (
"fmt"
"io/ioutil"
"os"
"strings"
)
func DupLinesInFiles1() {
counts := make(map[string]int)
for _, file := range os.Args[1:] {
data, err := ioutil.ReadFile(file)
if err != nil {
fmt.Fprintf(os.Stderr, "dup lines in file %s, error: %v\n", file, 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)
}
}
}
func main() {
DupLinesInFiles1()
}
实践：并发获取URL
fetch.go
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, "get url (%s) error: %s\n", url, err.Error())
os.Exit(1)
}
if resp.Body != nil {
defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
if err != nil {
fmt.Fprintf(os.Stderr, "get url (%s) reading error: %s\n", url, err.Error())
os.Exit(1)
}
fmt.Printf("%s", body)
}
}
}
go build fetch.go
./fetch http://localhost:8001
Get url PATH: /
并发
fetchall.go
package main
import (
"fmt"
"io/ioutil"
"net/http"
"os"
"time"
)
func fetch(url string, ch chan<- string) {
start := time.Now()
resp, err := http.Get(url)
if err != nil {
fmt.Fprintf(os.Stderr, "get url (%s) error: %s\n", url, err.Error())
os.Exit(1)
}
if resp.Body == nil {
fmt.Fprintf(os.Stderr, "get url (%s) error: %s\n", url, "response nil")
return
}
defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
if err != nil {
fmt.Fprintf(os.Stderr, "get url (%s) reading error: %s\n", url, err.Error())
os.Exit(1)
}
fmt.Printf("%s", body)
ch <- fmt.Sprintf("%.6f seconds %7d %s", time.Since(start).Seconds(), len(body), url)
}
func main() {
start := time.Now()
ch := make(chan string)
for _, url := range os.Args[1:] {
go fetch(url, ch)
}
for range os.Args[1:] {
fmt.Println(<-ch)
}
fmt.Printf("%.6f secondes elapsed\n", time.Since(start).Seconds())
}
go run fetchall.go
./fetchall http://localhost:8001 http://www.baidu.com
0.002738 seconds 16 http://localhost:8001
0.088088 seconds 285479 http://www.baidu.com
0.088129 secondes elapsed
实践：实现一个简单web服务器
server.go
package main
import (
"fmt"
"log"
"net/http"
)
func handler(w http.ResponseWriter, r *http.Request) {
// w.Write([]byte(r.URL.Path))
fmt.Fprintf(w, "Get url PATH: %s\n", r.URL.Path)
}
func main() {
http.HandleFunc("/", handler)
log.Fatal(http.ListenAndServe("localhost:8001", nil))
}
go build server.go ./server &
curl localhost:8001/
Get url PATH: /
refs
《The Go Programming Language》Alan A.A， Donovan & Brian W.Kernighan