package main
import (
"bufio"
"fmt"
"io"
"os"
)
func check(e error) {
if e != nil {
panic(e)
}
}
func main() {
dat, err := os.ReadFile("/tmp/dat")
check(err)
fmt.Print(string(dat))
f, err := os.Open("/tmp/dat")
check(err)
b1 := make([]byte, 5)
n1, err := f.Read(b1)
check(err)
fmt.Printf("%d bytes: %s\n", n1, string(b1[:n1]))
o2, err := f.Seek(6, 0)
check(err)
b2 := make([]byte, 2)
n2, err := f.Read(b2)
check(err)
fmt.Printf("%d bytes @ %d: ", n2, o2)
fmt.Printf("%v\n", string(b2[:n2]))
o3, err := f.Seek(6, 0)
check(err)
b3 := make([]byte, 2)
n3, err := io.ReadAtLeast(f, b3, 2)
check(err)
fmt.Printf("%d bytes @ %d: %s\n", n3, o3, string(b3))
_, err = f.Seek(0, 0)
check(err)
r4 := bufio.NewReader(f)
b4, err := r4.Peek(5)
check(err)
fmt.Printf("5 bytes: %s\n", string(b4))
f.Close()
}$ echo "hello" > /tmp/dat
$ echo "go" >> /tmp/dat
$ go run reading-files.go
hello
go
5 bytes: hello
2 bytes @ 6: go
2 bytes @ 6: go
5 bytes: hello