LESSON 374 OF 404 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: wc v4 — Mode Flag in Go

Practice

Combine the previous three versions of wc. Given a list of lines and a mode flag, return the requested count(s) as a string. This is our own simplified interface, not the real wc flags: the real tool combines flags (such as -lw) and pads its columns with spaces.

Function signature:

func wc(lines []string, mode string) string

Mode values:

"l" → line count, as a string.
"w" → word count (whitespace-separated tokens), as a string.
"c" → character count (lines only, no separating newlines), as a string.
"all" → lines + "\t" + words + "\t" + chars.

The "c" count is the one from v3 (the sum of the line lengths, no newlines). Any other mode value, for example "x" or "L" (modes are case-sensitive), gives the same result as "all". For an empty list, "l", "w" and "c" give "0" and "all" gives "0<TAB>0<TAB>0". The input is plain ASCII text.

Example:

Input: lines = ["hello", "world"], mode = "all"

Output: "2\t2\t10"

2 lines, 2 words (one per line), 10 characters total.

Compute all three counts in a single pass through lines, then branch on mode to pick the return value. strings.Fields handles the word count for you.

numLines := len(lines)
numWords := 0
numChars := 0
for _, line := range lines {
    numWords += len(strings.Fields(line))
    numChars += len(line)
}

Use strconv.Itoa(int) to convert numbers to strings.

The full solution:

func wc(lines []string, mode string) string {
    numLines := len(lines)
    numWords := 0
    numChars := 0
    for _, line := range lines {
        numWords += len(strings.Fields(line))
        numChars += len(line)
    }
    if mode == "l" { return strconv.Itoa(numLines) }
    if mode == "w" { return strconv.Itoa(numWords) }
    if mode == "c" { return strconv.Itoa(numChars) }
    return fmt.Sprintf("%d\t%d\t%d", numLines, numWords, numChars)
}

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CLI Tool: wc v4 — Mode Flag in Go

Wc V4 in Go