To read all file content(in bytes) to memory, ioutil.ReadAll
package main
import (
"fmt"
"io/ioutil"
"os"
"log"
)
func main() {
file, err := os.Open("file.txt")
if err != nil {
log.Fatal(err)
}
defer file.Close()
b, err := ioutil.ReadAll(file)
fmt.Print(b)
}
But sometimes, if the file size is big, it might be more memory-efficient to just read in chunks: buffer-size, hence you could use the implementation of io.Reader.Read from *os.File
func main() {
file, err := os.Open("file.txt")
if err != nil {
log.Fatal(err)
}
defer file.Close()
buf := make([]byte, 32*1024) // define your buffer size here.
for {
n, err := file.Read(buf)
if n > 0 {
fmt.Print(buf[:n]) // your read buffer.
}
if err == io.EOF {
break
}
if err != nil {
log.Printf("read %d bytes: %v", n, err)
break
}
}
}
Otherwise, you could also use the standard util package: bufio, try Scanner. A Scanner reads your file in tokens: separator.
By default, scanner advances the token by newline (of course you can customise how scanner should tokenise your file, learn from here the bufio test).
package main
import (
"fmt"
"os"
"log"
"bufio"
)
func main() {
file, err := os.Open("file.txt")
if err != nil {
log.Fatal(err)
}
defer file.Close()
scanner := bufio.NewScanner(file)
for scanner.Scan() { // internally, it advances token based on sperator
fmt.Println(scanner.Text()) // token in unicode-char
fmt.Println(scanner.Bytes()) // token in bytes
}
}
Lastly, I would also like to reference you to this awesome site: go-lang file cheatsheet. It encompassed pretty much everything related to working with files in go-lang, hope you'll find it useful
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