Add else block

src/day_2/shell_scripting.md

@@ -227,7 +227,7 @@ In our first bash script, we check for equality of two variables with a double e
 
 Speaking about syntax: You have to take spaces seriously with conditions.
 
-For example, if we define the variable `VAR=1`, the following snippets **do not work**:
+For example, if we define the variable `VAR=1`, the following snippets **do not work** (or have an unexpected behavior):
 
 1. No space after `[`
    ```bash
@@ -258,17 +258,7 @@ For example, if we define the variable `VAR=1`, the following snippets **do not
        echo "VAR has the value 1"
    fi
    ```
-
+1. No space before `==` and after `==`
-But the following snippets **work**:
-
-1. Space after `[`, before `]`, before `==` and after `==`
-   ```bash
-   if [ $VAR == 1 ]
-   then
-       echo "VAR has the value 1"
-   fi
-   ```
-1. Space after `[` and before `]`. No space before `==` and after `==`
    ```bash
    if [ $VAR==1 ]
    then
@@ -276,8 +266,42 @@ But the following snippets **work**:
    fi
    ```
 
+But the following snippet **work**:
+
+- Space after `[`, before `]`, before `==` and after `==`
+  ```bash
+  if [ $VAR == 1 ]
+  then
+       echo "VAR has the value 1"
+  fi
+  ```
+
 ### `else` block
 
+The `else` block runs commands inside it only if the condition is not true. The syntax is:
+
+```bash
+if [ CONDITION ]
+then
+    # Runs only if CONDITION is true
+    (...)
+else
+    # Runs only if CONDITION is false
+    (...)
+fi
+```
+
+Example:
+
+```bash
+if [ $VAR == 1 ]
+then
+    echo "VAR has the value 1"
+else
+    echo "VAR does not have the value 1"
+fi
+```
+
 <!-- TODO: else -->
 
 <!-- TODO: else if -->