LESSON 378 OF 404 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: grep v4 — Whole Word Match in Go

Practice

Build the -w flag of the Unix grep command. Given a list of lines and a search pattern (a single word made of letters, digits, and underscores), return all lines that contain pattern as a WHOLE word — i.e. the characters immediately before and after the match must NOT be word characters (letters, digits, or underscores). The match is case-sensitive.

Return the matching lines joined by newline characters (\n).

Function signature:

func grepWord(lines []string, pattern string) string

Example:

Input:
pattern = "cat"
lines = ["cat sat", "concat", "the cat", "category"]

Output: "cat sat\nthe cat"

When printed:
cat sat
the cat

Notice that "concat" is rejected because cat is preceded by the word character n (con|cat), and "category" is rejected because cat is followed by the word character e.

A line may contain the pattern more than once. It is selected if at least one occurrence is a whole word: with pattern "cat", the line "concat cat" is selected because of its second cat. The lines contain only ASCII characters.

If no lines match, return the empty string "".

Go's regexp package supports the \b word-boundary anchor. Wrap the pattern itself with regexp.QuoteMeta to escape any regex metacharacters.

re := regexp.MustCompile("\\b" + regexp.QuoteMeta(pattern) + "\\b")
// per line: if re.MatchString(line) keep

The full solution:

func grepWord(lines []string, pattern string) string {
    result := []string{}
    re := regexp.MustCompile("\\b" + regexp.QuoteMeta(pattern) + "\\b")
    for i := 0; i < len(lines); i++ {
        if re.MatchString(lines[i]) {
            result = append(result, lines[i])
        }
    }
    return strings.Join(result, "\n")
}

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CLI Tool: grep v4 — Whole Word Match in Go

Grep V4 in Go