Reading lines in Go

bufio.Scanner walks a reader line by line, and its error needs checking.

func countLines(input string) (int, int, error) {
    scanner := bufio.NewScanner(strings.NewReader(input))
    scanner.Buffer(make([]byte, 0, 64*1024), 1024*1024)

    lines, words := 0, 0
    for scanner.Scan() {
        line := strings.TrimSpace(scanner.Text())
        if line == "" {
            continue
        }
        lines++
        words += len(strings.Fields(line))
    }
    if err := scanner.Err(); err != nil {
        return 0, 0, fmt.Errorf("scan: %w", err)
    }
    return lines, words, nil
}

How it works

1. Scan returns false at the end or on an error.
2. Err afterwards distinguishes the two.
3. Buffer raises the limit for very long lines.

Keywords and builtins used here

• byte
• continue
• error
• for
• func
• if
• int
• len
• make
• return
• string

The run, in numbers

Lines

18

Characters to type

420

Tokens

129

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 74 seconds.

Type this snippet

Step 1 of 3 in Files & IO, step 6 of 26 in Standard library & project layout.

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Reading lines in other languages

• JavaScript