Files in Go

Read a whole file, write one, or open it and defer the close.

func writeThenRead(dir string) (string, error) {
    path := filepath.Join(dir, "runs.txt")
    if err := os.WriteFile(path, []byte("go 104\n"), 0o600); err != nil {
        return "", fmt.Errorf("write: %w", err)
    }

    file, err := os.Open(path)
    if err != nil {
        return "", fmt.Errorf("open: %w", err)
    }
    defer file.Close()

    info, err := file.Stat()
    if err != nil {
        return "", fmt.Errorf("stat: %w", err)
    }

    data, err := io.ReadAll(file)
    if err != nil {
        return "", fmt.Errorf("read: %w", err)
    }
    text := strings.TrimSpace(string(data))
    return fmt.Sprintf("%d bytes: %s", info.Size(), text), nil
}

How it works

1. os.ReadFile and os.WriteFile cover the simple cases.
2. defer file.Close() goes right after the error check.
3. The mode argument matters on the write path.

Keywords and builtins used here

• byte
• defer
• error
• func
• if
• return
• string

The run, in numbers

Lines

24

Characters to type

575

Tokens

173

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 99 seconds.

Type this snippet

Step 2 of 3 in Files & IO, step 7 of 26 in Standard library & project layout.

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