LESSON 381 OF 410 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: grep v1 — Substring Match in Java

Practice

Build a tiny version of the Unix grep command. Given a list of lines and a search pattern, return all lines that contain pattern as a substring (case-sensitive), joined by newline characters (\n).

Function signature:

public String grep(List<String> lines, String pattern)

Example:

Input:
pattern = "err"
lines = ["error: foo", "warning", "another error", "ok"]

Output: "error: foo\nanother error"

When printed:
error: foo
another error

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

Note: real grep treats the pattern as a regular expression by default (grep -F matches plain text). Here the pattern is always plain text: just look for it literally, so characters such as . or * mean nothing special.

Iterate over the lines, keep the ones where line.contains(pattern) is true, then String.join("\n", result).

The full solution:

class Solution {
    public String grep(List<String> lines, String pattern) {
        List<String> result = new ArrayList<>();
        for (String line : lines) {
            if (line.contains(pattern)) {
                result.add(line);
            }
        }
        return String.join("\n", result);
    }
}

STEP 1 OF 5

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CLI Tool: grep v1 — Substring Match in Java

Grep V1 in Java