Add new exercise grep (#752)

* Add exercise grep

Co-authored-by: Derk-Jan Karrenbeld <derk-jan+github@karrenbeld.info>

Author: TomPradat

config.json

@@ -1430,6 +1430,18 @@
         "strings"
       ],
       "deprecated": true
+    },
+    {
+      "slug": "grep",
+      "uuid": "78bcbae1-a0f2-460c-ba89-e51844fe9397",
+      "core": false,
+      "unlocked_by": "matrix",
+      "difficulty": 4,
+      "topics": [
+        "files",
+        "searching",
+        "text_formatting"
+      ]
     }
   ]
 }

exercises/grep/.eslintrc

@@ -0,0 +1,26 @@
+{
+  "root": true,
+  "parser": "babel-eslint",
+  "parserOptions": {
+    "ecmaVersion": 7,
+    "sourceType": "module"
+  },
+  "env": {
+    "es6": true,
+    "node": true,
+    "jest": true
+  },
+  "extends": [
+    "eslint:recommended",
+    "plugin:import/errors",
+    "plugin:import/warnings"
+  ],
+  "rules": {
+    "linebreak-style": "off",
+
+    "import/extensions": "off",
+    "import/no-default-export": "off",
+    "import/no-unresolved": "off",
+    "import/prefer-default-export": "off"
+  }
+}

exercises/grep/README.md

@@ -0,0 +1,102 @@
+# Grep
+
+Search a file for lines matching a regular expression pattern. Return the line
+number and contents of each matching line.
+
+The Unix [`grep`](http://pubs.opengroup.org/onlinepubs/9699919799/utilities/grep.html) command can be used to search for lines in one or more files
+that match a user-provided search query (known as the *pattern*).
+
+The `grep` command takes three arguments:
+
+1. The pattern used to match lines in a file.
+2. Zero or more flags to customize the matching behavior.
+3. One or more files in which to search for matching lines.
+
+Your task is to implement the `grep` function, which should read the contents
+of the specified files, find the lines that match the specified pattern
+and then output those lines as a single string. Note that the lines should
+be output in the order in which they were found, with the first matching line
+in the first file being output first.
+
+As an example, suppose there is a file named "input.txt" with the following contents:
+
+```text
+hello
+world
+hello again
+```
+
+If we were to call `grep "hello" input.txt`, the returned string should be:
+
+```text
+hello
+hello again
+```
+
+### Flags
+
+As said earlier, the `grep` command should also support the following flags:
+
+- `-n` Print the line numbers of each matching line.
+- `-l` Print only the names of files that contain at least one matching line.
+- `-i` Match line using a case-insensitive comparison.
+- `-v` Invert the program -- collect all lines that fail to match the pattern.
+- `-x` Only match entire lines, instead of lines that contain a match.
+
+If we run `grep -n "hello" input.txt`, the `-n` flag will require the matching
+lines to be prefixed with its line number:
+
+```text
+1:hello
+3:hello again
+```
+
+And if we run `grep -i "HELLO" input.txt`, we'll do a case-insensitive match,
+and the output will be:
+
+```text
+hello
+hello again
+```
+
+The `grep` command should support multiple flags at once.
+
+For example, running `grep -l -v "hello" file1.txt file2.txt` should
+print the names of files that do not contain the string "hello".
+
+## Setup
+
+Go through the setup instructions for Javascript to install the necessary
+dependencies:
+
+[https://exercism.io/tracks/javascript/installation](https://exercism.io/tracks/javascript/installation)
+
+## Requirements
+
+Install assignment dependencies:
+
+```bash
+$ npm install
+```
+
+## Making the test suite pass
+
+Execute the tests with:
+
+```bash
+$ npm test
+```
+
+In the test suites all tests but the first have been skipped.
+
+Once you get a test passing, you can enable the next one by changing `xtest` to
+`test`.
+
+## Source
+
+Conversation with Nate Foster. [http://www.cs.cornell.edu/Courses/cs3110/2014sp/hw/0/ps0.pdf](http://www.cs.cornell.edu/Courses/cs3110/2014sp/hw/0/ps0.pdf)
+
+## Submitting Incomplete Solutions
+
+It's possible to submit an incomplete solution so you can see how others have
+completed the exercise.

exercises/grep/babel.config.js

@@ -0,0 +1,14 @@
+module.exports = {
+  presets: [
+    [
+      '@babel/env',
+      {
+        targets: {
+          node: 'current',
+        },
+        useBuiltIns: false,
+      },
+
+    ],
+  ],
+};

exercises/grep/data/iliad.txt

@@ -0,0 +1,9 @@
+Achilles sing, O Goddess! Peleus' son;
+His wrath pernicious, who ten thousand woes
+Caused to Achaia's host, sent many a soul
+Illustrious into Ades premature,
+And Heroes gave (so stood the will of Jove)
+To dogs and to all ravening fowls a prey,
+When fierce dispute had separated once
+The noble Chief Achilles from the son
+Of Atreus, Agamemnon, King of men.

exercises/grep/data/midsummer-night.txt

@@ -0,0 +1,7 @@
+I do entreat your grace to pardon me.
+I know not by what power I am made bold,
+Nor how it may concern my modesty,
+In such a presence here to plead my thoughts;
+But I beseech your grace that I may know
+The worst that may befall me in this case,
+If I refuse to wed Demetrius.

exercises/grep/data/paradise-lost.txt

@@ -0,0 +1,8 @@
+Of Mans First Disobedience, and the Fruit
+Of that Forbidden Tree, whose mortal tast
+Brought Death into the World, and all our woe,
+With loss of Eden, till one greater Man
+Restore us, and regain the blissful Seat,
+Sing Heav'nly Muse, that on the secret top
+Of Oreb, or of Sinai, didst inspire
+That Shepherd, who first taught the chosen Seed

exercises/grep/example.js

@@ -0,0 +1,95 @@
+#!/usr/bin/env node
+const fs = require("fs");
+
+// Helpers
+const availables_options = [
+  "n", // add line numbers
+  "l", // print file names where pattern is found
+  "i", // ignore case
+  "v", // reverse files results
+  "x" // match entire line
+];
+
+const does_line_matche_pattern = (line, pattern) => {
+  let left = line;
+  let right = pattern;
+
+  if (is_option_set("i")) {
+    left = line.toLowerCase();
+    right = pattern.toLowerCase();
+  }
+
+  if (is_option_set("x")) {
+    return left === right;
+  }
+
+  return left.match(right) !== null;
+};
+
+const getConfigFromArgs = () => {
+  const config = {
+    pattern: "",
+    options: [],
+    files: []
+  };
+
+  let has_pattern_been_found = false;
+
+  process.argv.slice(2).forEach(val => {
+    if (has_pattern_been_found) {
+      config.files.push(val);
+    } else if (val.indexOf("-") !== -1) {
+      const option = val.replace("-", "");
+
+      if (!availables_options.includes(option)) {
+        throw new Error(`Unknown option ${option}`);
+      }
+
+      config.options.push(option);
+    } else {
+      has_pattern_been_found = true;
+      config.pattern = val;
+    }
+  });
+
+  return config;
+};
+
+const config = getConfigFromArgs();
+const is_option_set = option => config.options.includes(option);
+
+// Actual script
+config.files.forEach(file => {
+  const data = fs.readFileSync(file, { encoding: "utf-8" });
+
+  if (is_option_set("l")) {
+    data.split("\n").find(line => {
+      const does_line_match_pattern = does_line_matche_pattern(line, config.pattern);
+
+      return is_option_set("v") ? !does_line_match_pattern : does_line_match_pattern;
+    }) && console.log(file);
+  } else {
+    data.split("\n").forEach((line, index) => {
+      let result = "";
+      let should_output_line = does_line_matche_pattern(line, config.pattern);
+
+      if (is_option_set("v")) {
+        should_output_line = !should_output_line;
+      }
+
+      if (should_output_line) {
+        if (config.files.length > 1) {
+          result += `${file}:`;
+        }
+
+        if (is_option_set("n")) {
+          result += `${index + 1}:`;
+        }
+
+        result += line;
+
+        console.log(result);
+      }
+    });
+  }
+});

exercises/grep/grep.js

@@ -0,0 +1,15 @@
+#!/usr/bin/env node
+
+// The above line is a shebang. On Unix-like operating systems, or environments, this will allow the script to be
+// run by node, and thus turn this JavaScript file into an executable. If you don't have a Unix-like operating
+// system or environment, for example Windows without WSL, you can use 
+//
+// node grep.js args
+//
+// Instead of "./grep.js args".
+// 
+// Read more about shebangs here: https://en.wikipedia.org/wiki/Shebang_(Unix)
+// 
+// This is only a SKELETON file for the 'Grep' exercise. It's been provided as a
+// convenience to get you started writing code faster.
+//