codecrafters-io · UdeshyaDhungana · Nov 11, 2025 · Nov 11, 2025 · Nov 11, 2025 · Nov 11, 2025
diff --git a/.gitignore b/.gitignore
@@ -1,2 +1,5 @@
 course-definition-tester
 .history/
+
+## MacOS
+.DS_Store
diff --git a/course-definition.yml b/course-definition.yml
@@ -76,6 +76,16 @@ extensions:
       Along the way, you'll learn about how to implement the `*` quantifier (zero or more), and bounded quantifiers.
       [1]: https://learn.microsoft.com/en-us/dotnet/standard/base-types/quantifiers-in-regular-expressions
 
+  - slug: "highlighting"
+    name: "Highlighting"
+    description_markdown: |
+      In this challenge extension, you'll add support for [highlighting][1] to your Grep implementation.
+
+      Along the way, you'll learn about [ANSI escape codes][2], and more.
+
+      [1]: https://linuxcommando.blogspot.com/2007/10/grep-with-color-output.html
+      [2]: https://en.wikipedia.org/wiki/ANSI_escape_code
+
 stages:
   - slug: "cq2"
     name: "Match a literal character"
@@ -304,3 +314,39 @@ stages:
     difficulty: hard
     marketing_md: |-
       In this stage, we'll add support for `{n,m}`, the [between n and m times](https://docs.microsoft.com/en-us/dotnet/standard/base-types/quantifiers-in-regular-expressions#match-between-n-and-m-times-nm) quantifier.
+
+  # Highlighting
+  - slug: "bm2"
+    primary_extension_slug: "highlighting"
+    name: "Highlighting a single match"
+    difficulty: hard
+    marketing_md: |-
+      In this stage, you'll add support for highlighting a single match in your grep implementation.
+
+  - slug: "eq0"
+    primary_extension_slug: "highlighting"
+    name: "Highlighting multiple matches"
+    difficulty: hard
+    marketing_md: |-
+      In this stage, you'll add support for highlighting multiple matches in your grep implementation.
+
+  - slug: "jk4"
+    primary_extension_slug: "highlighting"
+    name: "Disabling highlighting"
+    difficulty: easy
+    marketing_md: |-
+      In this stage, you'll add support for disabling the highlighting in your grep implementation using the `never` coloring option.
+
+  - slug: "na5"
+    primary_extension_slug: "highlighting"
+    name: "Auto highlighting option"
+    difficulty: medium
+    marketing_md: |-
+      In this stage, you'll add support for `auto` coloring option in the `--color` flag in your grep implementation.
+
+  - slug: "nd0"
+    primary_extension_slug: "highlighting"
+    name: "Default highlighting behavior"
+    difficulty: easy
+    marketing_md: |-
+      In this stage, you'll implement the `auto` coloring option as the default coloring option when the `--color` flag is not present.
diff --git a/stage_descriptions/highlighting-01-bm2.md b/stage_descriptions/highlighting-01-bm2.md
@@ -0,0 +1,92 @@
+In this stage, you'll add support for highlighting a single match in your grep implementation.
+
+### Highlighting the matched text
+
+When `--color=always` option is used with grep, it always highlights the matched text in its output.
+
+Example usage:
+
+<html>
+<pre>
+<code>$ echo -n "I have 1 apple" | grep --color=always -E '\d'
+I have <span style="color: red; font-weight: bold;">1</span> apple</code>
+</pre>
+</html>
+
+Grep uses [ANSI escape sequences](https://en.wikipedia.org/wiki/ANSI_escape_code) to add color to terminal output. These are special character sequences that terminals interpret as formatting commands rather than regular text.
+
+The default color used by grep for the matched text is bold red. For example, grep uses the following ANSI escape sequences for wrapping the matched text:
+
+```
+\033[01;31m\033[K
+...
+\033[m\033[K
+```
+
+**Exaple Opening Sequence: `\033[01;31m\033[K`**
+
+| Component | Meaning |
+|-----------|---------|
+| `\033` | Escape character that introduces the ANSI control sequence |
+| `[` | Start marker for [Select Graphic Rendition (SGR)](https://vt100.net/docs/vt510-rm/SGR.html) parameters |
+| `01;31` | SGR codes: `01` = bold/bright text, `31` = red foreground color (separated by `;`) |
+| `m` | Terminates the SGR sequence |
+|  |
+| `\033` | Escape character that introduces the ANSI control sequence |
+| `[` | Start marker for SGR parameters |
+| `K` | Erase all characters to the right of the cursor |
+
+**Example Closing Sequence: `\033[m\033[K`**
+
+| Component | Meaning |
+|-----------|---------|
+| `\033` | Escape character that introduces the ANSI control sequence |
+| `[` | Start marker for SGR parameters |
+| *(empty)* | No parameters = reset all attributes to default |
+| `m` | Terminates the SGR sequence |
+|   |
+| `\033` | Escape character that introduces the ANSI control sequence
+| `[` | Start marker for SGR parameters |
+| `K` | Erase all characters to the right of the cursor |
+
+When the SGR parameter is `0` or is not present (empty), it resets all attributes so that the rest of the text will be printed without any highlights.
+
+### Tests
+
+The tester will execute your program like this:
+
+<html>
+<pre>
+<code>$ echo -n "I have 3 apples" | grep --color=always -E '\d'
+I have <span style="font-weight:bold; color:red;">3</span> apples</code>
+</pre>
+</html>
+
+If the input does not match the pattern, your program must:
+- Exit with the code 1
+- Exit with no printed output
+
+If the input text matches the pattern, your program must:
+- Exit with the code 0
+- Print the input text to the standard output
+- Highlight the matched text in the input using the grep's default color.
+
+### Notes
+
+1. You only need to handle the case of single match. We'll get to highlighting multiple matches in the next stage.
+
+2. The matched text should highlighted using the bold (`01`) and red (`31`) attributes. You may use any combination of ANSI codes to achieve this highlighting effect. For example, to produce the following output:
+
+<html>
+<pre>
+<code>hello<span style="color:red; font-weight:bold" >matched</span>world</code>
+</pre>
+</html>
+
+Any of the following sequences can be used
+
+```
+hello\033[31;01m\033[Kmatched\033[m\033[Kworld
+hello\033[31;01m\033[K\033[Kmatched\033[m\033[K\033[Kworld
+hello\033[01;31m\033[Kmatched\033[m\033[Kworld
+```
diff --git a/stage_descriptions/highlighting-02-eq0.md b/stage_descriptions/highlighting-02-eq0.md
@@ -0,0 +1,42 @@
+In this stage, you'll add support for highlighting multiple matches in your grep implementation.
+
+### Highlighting multiple matches
+
+Grep highlights all the matching texts it can find in each line.
+
+Example usage:
+
+<html>
+<pre>
+<code>$ echo -n "dogs and cats are pets" | grep --color=always -E '(dogs|cats)'
+<span style="color: red; font-weight: bold;">dogs</span> and <span style="color: red; font-weight: bold;">cats</span> are pets</code>
+</pre>
+</html>
+
+### Tests
+
+The tester will execute your program like this:
+
+<html>
+<pre>
+<code>$ echo -n "jekyll and hyde" | grep --color=always -E '(jekyll|hyde)'
+<span style="color: red; font-weight: bold;">jekyll</span> and <span style="color: red; font-weight: bold;">hyde</span>
+<br />
+$ echo -n "2025" | grep --color=always -E '\d'
+<span style="color: red; font-weight: bold;">2025</span></code></pre>
+</html>
+
+If the input does not match the pattern, your program must:
+- Exit with the code 1
+- Exit with no printed output
+
+If the input text matches the pattern, your program must:
+- Exit with the code 0
+- Print the input text to the standard output
+- Highlight all the matched texts in the input using the grep's default color.
+
+### Notes
+
+- The tester accepts multiple valid ANSI-encoded representations of the same highlighted text. To display the bold red text: <span style="color: red; font-weight: bold;">2025</span>, any equivalent combination is acceptable. Example of valid ANSI sequences:
+    - `\u001b[1;31m2025\u001b[0m`
+    - `\u001b[1;31m20\u001b[0m\u001b[1;31m25\u001b[0m`
diff --git a/stage_descriptions/highlighting-03-jk4.md b/stage_descriptions/highlighting-03-jk4.md
@@ -0,0 +1,30 @@
+In this stage, you'll add support for disabling the highlighting in your grep implementation using the `never` coloring option.
+
+### The `--color=never` option
+
+When a line is matched, grep only prints the matched line to the standard output. It does not highlight the matched text.
+
+Example usage:
+
+```bash
+$ echo -n "Sally has 3 parrots" | grep --color=never -E "par+ots?"
+Sally has 3 parrots
+```
+
+### Tests
+
+The tester will execute your program like this:
+
+```bash
+$ echo -n "I have 5 vegetables" | grep --color=never -E '\d'
+I have 5 vegetables
+```
+
+If the input matches the pattern, your program must:
+- Exit with the code 0
+- Print the input line to the standard output
+- No highlights should be placed in the output text because `--color=never` option is being used.
+
+If the input does not match the pattern, your program must:
+- Exit with the code 1
+- Exit with no printed output
diff --git a/stage_descriptions/highlighting-04-na5.md b/stage_descriptions/highlighting-04-na5.md
@@ -0,0 +1,82 @@
+In this stage, you'll add support for `auto` coloring option in the `--color` flag in your grep implementation.
+
+### The `auto` color option
+
+When `--color=auto` option is used with grep, it behaves in the following manner:
+
+- If the output stream is a [TTY device](https://www.ibm.com/docs/en/aix/7.1.0?topic=communications-tty-terminal-device), like the terminal, highlighting is enabled.
+
+- If the output stream is not a TTY device, for example, the output is piped to another command, or being redirected to a non-TTY device, highlighting is disabled.
+
+Example usage:
+
+<html>
+<pre>
+<code>$ echo -n "I have 3 cows" | grep --color=auto -E 'cows'
+I have <span style="font-weight:bold;color:red">3</span> cows
+$ echo -n "I have 4 cows" | grep --color=auto -E 'cows' >> /dev/tty
+I have <span style="font-weight:bold;color:red">4</span> cows</code>
+</pre>
+</html>
+
+The output text is highlighted in this case since the output in both cases is a TTY device.
+
+When the output stream is piped to another command, or redirected to a non-TTY device, the ANSI highlighting sequences are not placed in the output text.
+
+```bash
+# Output stream is piped to another command
+$ echo -n "I have 3 apples" | grep --color=auto -E '\d' | hexdump -C
+00000000  49 20 68 61 76 65 20 33  20 61 70 70 6c 65 73 0a  |I have 3 apples.|
+00000010
+
+# Output stream is redirected to a non-TTY device
+$ echo -n "I have 4 apples" | grep --color=auto -E '\d' >> output.txt
+
+$ hexdump -C output.txt
+00000000  49 20 68 61 76 65 20 34  20 61 70 70 6c 65 73 0a  |I have 4 apples.|
+00000010
+```
+
+### Tests
+
+The tester will execute your program like this:
+
+<html>
+<pre>
+<code>$ echo -n "I have 4 cats" | grep --color=auto -E 'cats'
+I have 4 <span style="color:red; font-weight:bold;">cats</span>
+$ echo -n "I have 5 cats" | grep --color=auto -E 'cats' >> /dev/tty
+I have 5 <span style="color:red; font-weight:bold;">cats</span></code>
+</pre>
+</html>
+
+If the input does not match the pattern, your program must:
+- Exit with the code 1
+
+If the input text matches the pattern, your program must:
+- Exit with the code 0
+- Print the input text to the standard output
+- The matched text in the output should be highlighted
+
+The tester will also execute your program like this:
+
+```bash
+# Redirection to a non-tty device
+$ echo -n "I have 3 horses" | grep --color=auto -E '\d' >> file.txt
+
+# Piping to another command
+$ echo -n "He has 9 rabbits" | grep --color=auto -E '\d' | another_command
+```
+
+For both of these cases,
+If the input does not match the pattern, your program must:
+- Exit with the code 1
+- Exit with no printed output
+
+If the input text matches the pattern, your program must exit with the code 0 and
+- The input text should be written to the file `file.txt`, or be supplied to another command, depending on the case.
+- The ANSI escape sequence for highlighting should not be present inside the file, or supplied to another command, depending on the case.
+
+### Notes
+
+- You might find it helpful to use the equivalent of [`isatty()`](https://man7.org/linux/man-pages/man3/isatty.3.html) function in your programming language to check whether the output stream is a TTY device.
diff --git a/stage_descriptions/highlighting-05-nd0.md b/stage_descriptions/highlighting-05-nd0.md
@@ -0,0 +1,69 @@
+In this stage, you'll implement the `auto` coloring option as the default coloring option when the `--color` flag is not present.
+
+### The default behavior
+
+When the `--color` flag is not present, it is equivalent of using grep with the `--color=auto` option.
+
+Example usage:
+
+<html>
+<pre>
+<code>$ echo -n "I have 3 cows" | grep -E 'cows'
+I have <span style="font-weight:bold;color:red">3</span> cows
+$ echo -n "I have 4 cows" | grep -E 'cows' >> /dev/tty
+I have <span style="font-weight:bold;color:red">4</span> cows</code>
+</pre>
+</html>
+
+The output text is highlighted in this case.
+
+When the output stream is piped to another command, or redirected to a non-TTY device, the ANSI highlighting sequences are not placed in the output text.
+
+```bash
+# Output stream is piped to another command
+$ echo -n "I have 3 apples" | grep --color=auto -E '\d' | hexdump -C
+00000000  49 20 68 61 76 65 20 33  20 61 70 70 6c 65 73 0a  |I have 3 apples.|
+00000010
+
+# Output stream is redirected to a non-TTY device
+$ echo -n "I have 4 apples" | grep --color=auto -E '\d' >> output.txt
+
+$ hexdump -C output.txt
+00000000  49 20 68 61 76 65 20 34  20 61 70 70 6c 65 73 0a  |I have 4 apples.|
+00000010
+```
+
+### Tests
+
+The tester will execute your program like this:
+
+```bash
+$ echo -n "I have 3 horses" | grep -E '\d'
+```
+
+If the input does not match the pattern, your program must:
+- Exit with the code 1
+- Exit with no printed output
+
+If the input text matches the pattern, your program must:
+- Exit with the code 0
+- Print the input text to the standard output
+- The matched text in the output should be highlighted
+
+The tester will also execute your program like this:
+
+```bash
+# Redirection to a non-tty device
+$ echo -n "I have 3 horses" | grep -E '\d' >> file.txt
+
+# Piping to another command
+$ echo -n "He has 9 rabbits" | grep -E '\d' | another_command
+```
+
+For both of these cases,
+If the input does not match the pattern, your program must:
+- Exit with the code 1
+
+If the input text matches the pattern, your program must exit with the code 0 and
+- The input text should be written to the file `file.txt`, or be supplied to another command, depending on the case.
+- The ANSI escape sequence for highlighting should not be present inside the file, or supplied to another command, depending on the case.