How to modify files in golang

The method for file modification in golang is: 1. Create a Go sample file; 2. Use the "os.OpenFile()" function to open the file to be modified and specify the opening method, permissions and other information; 3. Use "io.WriteString()" and other methods write data to the file; 4. After the modification is successful, use the "os.File.Sync()" function to synchronize the file content to the disk; 5. Call "file.Close()" Just close the file and print the results.

Operating system for this tutorial: Windows 10 system, Go1.20.1 version, Dell G3 computer.

The method for file modification in golang is:

1. Use the os.OpenFile() function to open the file to be modified, and specify the opening method, permissions and other information.

For example:

file, err := os.OpenFile("example.txt", os.O_RDWR, 0644)
if err != nil {
    log.Fatal(err)
}
defer file.Close()

In the above example, we opened the file "example.txt", and used os.O_RDWR to indicate that it was opened in read-write mode, and finally specified the file permission as 0644.

2. Use methods such as io.WriteString(), io.Write() or fmt.Fprintf() to write data to the file.

For example:

if _, err := io.WriteString(file, "Hello, World!"); err != nil {
    log.Fatal(err)
}

Here, we use the io.WriteString() function to write the string "Hello, World!" to the file, and the function return value is the written bytes number, and an exception will be thrown if an error occurs.

3. After the modification is successful, use the os.File.Sync() function to synchronize the file contents to the disk. For example:

if err := file.Sync(); err != nil {
    log.Fatal(err)
}

After the above operations are completed, the file can be closed. So this example needs to call file.Close() at the end.

The following is a code example for completely modifying the file:

package main
import (
    "io"
    "log"
    "os"
)
func main() {
    f, err := os.OpenFile("example.txt", os.O_RDWR, 0644)
    if err != nil {
        log.Fatal(err)
    }
    defer f.Close()
    if _, err := io.WriteString(f, "Hello, World!"); err != nil {
        log.Fatal(err)
    }
    if err := f.Sync(); err != nil {
        log.Fatal(err)
    }
}

The output result is that the content of the file example.txt is "Hello, World!".

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