exercises: minor edits

Author: robinengler

exercise_instructions.md

@@ -526,11 +526,20 @@ Using `ls` and wildcard characters, perform the following tasks:
    <br>
 
     ```sh
-    ls -l *l?[a-h]*_g*
+     ls -l *l?[a-h]*_g*
 
-    # Eubalaena_glacialis    (North Atlantic right whale).
-    # Gorilla_gorilla        (Western gorilla).
-    # Plecturocebus_grovesi  (Alta Floresta titi monkey - a New World monkey).
+     # There are 3 matches:
+     # Eubalaena_glacialis    (North Atlantic right whale).
+     # Gorilla_gorilla        (Western gorilla).
+     # Plecturocebus_grovesi  (Alta Floresta titi monkey - a New World monkey).
+    ```
+
+   Note that if we wanted to also match species with the pattern `l?[a-h]` at
+   the start of their genus name, we would need:
+
+    ```sh
+     # Returns the same 3 matches as above.
+     ls -l *[Ll]?[a-h]*_g*
     ```
 
    </details>
@@ -640,6 +649,7 @@ becomes useful.
 Enter the directory `exercise_3/` and perform the following tasks:
 
 1. **Create directories** with the **`mkdir`** command:
+
    * In the directory `exercise_3/`, create 2 new directories:
      `species_by_genus` and `species_by_common_name`.
    * In `species_by_genus/`, create 2 new subdirectories:
@@ -648,16 +658,20 @@ Enter the directory `exercise_3/` and perform the following tasks:
      `Crocidura` ([a genus of shrews](https://en.wikipedia.org/wiki/Crocidura)).
    * In `species_by_common_name/`, create 2 new subdirectories
      named `B` and `R`.
+  
+   <br>
 
-   > **🔥 Tip:** to avoid having to rewrite a command, remember that you can
-   > use the **up arrow** of your keyboard to go back in your terminal history.
+   > **🔥 Tip:**
+   >
+   > To avoid having to rewrite a command, remember that you can use the
+   > **up arrow** of your keyboard to go back in your terminal history.
    > This allows you to re-use a command that you wrote earlier, while making
    > changes to it if needed.
 
    <details><summary><b>✅ Solution</b></summary>
    <br>
 
-    * **Create directories `species_by_genus` and `species_by_common_name`**.
+   **Create directories `species_by_genus` and `species_by_common_name`**.
 
      ```sh
      cd exercise_3
@@ -673,7 +687,7 @@ Enter the directory `exercise_3/` and perform the following tasks:
      mkdir species_by_{genus,common_name}
      ```
 
-    * **Create subdirectories `Dendrolagus` and `Crocidura`**.
+   **Create subdirectories `Dendrolagus` and `Crocidura`**.
 
      ```sh
      # Option 1: create the subdirectories from the root of exercise_3.
@@ -688,7 +702,7 @@ Enter the directory `exercise_3/` and perform the following tasks:
      mkdir species_by_genus/{Dendrolagus,Crocidura}
      ```
 
-    * **Create subdirectories `B` and `R`**.
+   **Create subdirectories `B` and `R`**.
 
      ```sh
      # Option 1: specify the full (relative) path of the subdirectories to create.
@@ -703,22 +717,25 @@ Enter the directory `exercise_3/` and perform the following tasks:
      mkdir species_by_common_name/{B,R}
      ```
 
-    **✨ Note:** using the **`-p` option of `mkdir`**, it is possible to create
-    multiple levels of directories in a single command. For example, we could
-    create all the directories for this exercise in a single command:
-
-      ```sh
-      mkdir -p species_by_{genus/{Dendrolagus,Crocidura},common_name/{B,R}}
-      ```
-
-    **🔥 Tip:** to preview the output of a brace expansion (or filename
-    expansion), you can run the command prefixed with **`echo`**: this prints
-    the command that would be executed to the terminal without running the
-    command.
+   > **✨ Note:**
+   >
+   > Using the **`-p` option of `mkdir`**, it is possible to create multiple
+   > levels of directories in a single command. For example, we could create
+   > all the directories for this exercise in a single command:
+   >
+   > ```sh
+   > mkdir -p species_by_{genus/{Dendrolagus,Crocidura},common_name/{B,R}}
+   > ```
 
-      ```sh
-      echo mkdir -p species_by_{genus/{Dendrolagus,Crocidura},common_name/{B,R}}
-      ```
+   > **🔥 Tip:**
+   >
+   > To preview the output of a brace expansion (or filename expansion), you
+   > can run the command prefixed with **`echo`**: this prints the command
+   > that would be executed to the terminal without running the command.
+   >
+   > ```sh
+   > echo mkdir -p species_by_{genus/{Dendrolagus,Crocidura},common_name/{B,R}}
+   > ```
 
    </details>
    <br>
@@ -732,6 +749,7 @@ Enter the directory `exercise_3/` and perform the following tasks:
      [Red Wolf](https://en.wikipedia.org/wiki/Red_wolf) (_Canis rufus_) to the
      directory `species_by_common_name`.
 
+   <br>
    <details><summary><b>✅ Solution</b></summary>
    <br>