This article was originally published on GitHub.
Setup
$ go get golang.org/x/tools/cmd/goimports
...
$ mkdir go-handson
$ cd go-handson
Hello World
$ touch hello.go
// hello.go
package main
import (
"fmt"
)
func main() {
fmt.Println("Hello World!")
}
$ $GOPATH/bin/goimports -w .
# Format and add packages that should be imported
$ go run hello.go
Hello World!
$ go build -o hello .
$ ./hello
Hello World!
flag package
Usage of flag.StringVar
$ touch flag.go
// flag.go
package main
import (
"flag"
"fmt"
)
func main() {
var name string
flag.StringVar(&name, "opt", "", "Usage")
flag.Parse()
fmt.Println(name)
}
$ go run hello.go -opt option
option
If you want to know more about the flag package, please go to the https://golang.org/pkg/flag/
Exercise 1-1
Create a CLI application which outputs Hello World! if no options are specified. And if a string option is specified as -name, it has to output Hello [YOUR_NAME]!
$ go run hello.go
Hello World!
$ go run hello.go -name Gopher
Hello Gopher!
The answer is hello.go
os package
Usage of os.Args
$ touch args.go
// args.go
package main
import (
"fmt"
"os"
)
func main() {
fmt.Println(os.Args)
fmt.Println(os.Args[1])
}
$ go build -o args args.go
$ ./args Gopher
[./args Gopher]
Gopher
File I/O
Reading files
file, err := os.Open(`/path/to/file`)
if err != nil {
panic(err)
}
defer file.Close()
buf := make([]byte, BUFSIZE)
for {
n, err := file.Read(buf)
if n == 0 {
break
}
if err != nil {
panic(err)
}
fmt.Print(string(buf[:n]))
}
Writing files
f, err := os.Create("/path/to/file")
if err != nil {
panic(err)
}
defer f.Close()
b := []byte("Foo")
n, err := f.Write(b)
if err != nil {
panic(err)
}
fmt.Println(n)
Exercise 1-2
Create an application file.go which creates a file and write a string Hello Writing to Files! to it. And the file name has to be specified as a command line argument.
$ go run file.go file.txt
The number of bytes written: 23
$ cat file.txt
Hello Writing to Files!
The answer is file.go
Top comments (1)
Could you put your go tutorial in a series for ease of access, it's proving hard even with the part naming scheme.