Minor book improvements and shellcheck CI (#194)

Author: bobbyiliev

.github/workflows/shellcheck.yml

@@ -0,0 +1,26 @@
+name: ShellCheck eBook
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - "ebook/en/content/**"
+      - "scripts/shellcheck-ebook.sh"
+  pull_request:
+    paths:
+      - "ebook/en/content/**"
+      - "scripts/shellcheck-ebook.sh"
+
+jobs:
+  shellcheck:
+    name: Lint bash code blocks
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Install ShellCheck
+        run: sudo apt-get update && sudo apt-get install -y shellcheck
+
+      - name: Run ShellCheck on ebook code blocks
+        run: ./scripts/shellcheck-ebook.sh ebook/en/content

ebook/en/content/004-bash-variables.md

@@ -1,131 +1,167 @@
-# Bash Variables
-
-As in any other programming language, you can use variables in Bash Scripting as well. However, there are no data types, and a variable in Bash can contain numbers as well as characters.
-
-To assign a value to a variable, all you need to do is use the `=` sign:
-
-```bash
-name="DevDojo"
-```
-
->{notice} as an important note, you can not have spaces before and after the `=` sign.
-
-After that, to access the variable, you have to use the `$` and reference it as shown below:
-
-```bash
-echo $name
-```
-
-Wrapping the variable name between curly brackets is not required, but is considered a good practice, and I would advise you to use them whenever you can:
-
-```bash
-echo ${name}
-```
-
-The above code would output: `DevDojo` as this is the value of our `name` variable.
-
-Next, let's update our `devdojo.sh` script and include a variable in it.
-
-Again, you can open the file `devdojo.sh` with your favorite text editor, I'm using nano here to open the file:
-
-```bash
-nano devdojo.sh
-```
-
-Adding our `name` variable here in the file, with a welcome message. Our file now looks like this:
-
-```bash
-#!/bin/bash
-
-name="DevDojo"
-
-echo "Hi there $name"
-```
-
-Save it and run the file using the command below:
-
-```bash
-./devdojo.sh
-```
-
-You would see the following output on your screen:
-
-```bash
-Hi there DevDojo
-```
-
-Here is a rundown of the script written in the file:
-
-* `#!/bin/bash` - At first, we specified our shebang.
-* `name=DevDojo` - Then, we defined a variable called `name` and assigned a value to it.
-* `echo "Hi there $name"` - Finally, we output the content of the variable on the screen as a welcome message by using `echo`
-
-You can also add multiple variables in the file as shown below:
-
-```bash
-#!/bin/bash
-
-name="DevDojo"
-greeting="Hello"
-
-echo "$greeting $name"
-```
-
-Save the file and run it again:
-
-```bash
-./devdojo.sh
-```
-
-You would see the following output on your screen:
-
-```bash
-Hello DevDojo
-```
-Note that you don't necessarily need to add semicolon `;` at the end of each line. It works both ways, a bit like other programming language such as JavaScript!
-
-
-You can also add variables in the Command Line outside the Bash script and they can be read as parameters:
-
-```bash
-./devdojo.sh Bobby buddy!
-```
-This script takes in two parameters `Bobby`and `buddy!` separated by space. In the `devdojo.sh` file we have the following:
-
-```bash
-#!/bin/bash
-
-echo "Hello there" $1
-
-```
-`$1` is the first input (`Bobby`) in the Command Line. Similarly, there could be more inputs and they are all referenced to by the `$` sign and their respective order of input. This means that `buddy!` is referenced to using `$2`. Another useful method for reading variables is the `$@` which reads all inputs.
-
-So now let's change the `devdojo.sh` file to better understand: 
-
-```bash
-#!/bin/bash
-
-echo "Hello there" $1
-
-# $1 : first parameter
-
-echo "Hello there" $2
-
-# $2 : second parameter
-
-echo "Hello there" $@
-
-# $@ : all
-```
-The output for:
-
-```bash
-./devdojo.sh Bobby buddy!
-``` 
-Would be the following:
-
-```bash
-Hello there Bobby
-Hello there buddy!
-Hello there Bobby buddy!
-```
+# Bash Variables
+
+As in any other programming language, you can use variables in Bash Scripting as well. However, there are no data types, and a variable in Bash can contain numbers as well as characters.
+
+To assign a value to a variable, all you need to do is use the `=` sign:
+
+```bash
+name="DevDojo"
+```
+
+>{notice} as an important note, you can not have spaces before and after the `=` sign.
+
+After that, to access the variable, you have to use the `$` and reference it as shown below:
+
+```bash
+echo "$name"
+```
+
+The above code would output: `DevDojo` as this is the value of our `name` variable.
+
+## Quoting variables
+
+You should **always wrap variable references in double quotes** (`"$name"`). This is one of the most important habits to develop in Bash scripting. Without quotes, Bash will perform **word splitting** and **globbing** on the variable's value, which leads to bugs and even security vulnerabilities.
+
+Here is an example of what can go wrong without quotes:
+
+```bash
+#!/bin/bash
+
+filename="my file.txt"
+
+# Wrong - Bash splits this into two words: "my" and "file.txt"
+touch $filename    # Creates two files: "my" and "file.txt"
+
+# Correct - the quotes preserve the value as a single argument
+touch "$filename"  # Creates one file: "my file.txt"
+```
+
+Without quotes, if a variable contains spaces, wildcards (`*`, `?`), or other special characters, Bash will interpret them rather than treating the value as a single string. This can cause scripts to break or behave unpredictably.
+
+>{notice} **Rule of thumb:** Always use double quotes around variables: `"$name"`, not `$name`. The only common exception is inside `[[ ]]` test brackets, where word splitting does not occur, but even there quoting is a good habit.
+
+## When to use curly braces
+
+You can also wrap the variable name in curly braces: `${name}`. This is **required** when the variable name is followed by characters that could be interpreted as part of the name:
+
+```bash
+greeting="Hello"
+
+# Without braces, Bash looks for a variable called $greetings (not $greeting)
+echo "$greetings world"   # Prints: " world" (empty - no such variable)
+
+# With braces, Bash knows the variable name is just "greeting"
+echo "${greeting}s world" # Prints: "Hellos world"
+```
+
+Curly braces are also required for arrays (`${array[0]}`), string slicing (`${name:0:3}`), and default values (`${name:-default}`). For simple cases like `echo "$name"`, the braces are optional, so both `"$name"` and `"${name}"` work.
+
+Throughout this book, we use curly braces when they are needed for clarity or disambiguation, and omit them when the variable stands alone.
+
+## Using variables in a script
+
+Next, let's update our `devdojo.sh` script and include a variable in it.
+
+Again, you can open the file `devdojo.sh` with your favorite text editor, I'm using nano here to open the file:
+
+```bash
+nano devdojo.sh
+```
+
+Adding our `name` variable here in the file, with a welcome message. Our file now looks like this:
+
+```bash
+#!/bin/bash
+
+name="DevDojo"
+
+echo "Hi there $name"
+```
+
+Save it and run the file using the command below:
+
+```bash
+./devdojo.sh
+```
+
+You would see the following output on your screen:
+
+```bash
+Hi there DevDojo
+```
+
+Here is a rundown of the script written in the file:
+
+* `#!/bin/bash` - At first, we specified our shebang.
+* `name="DevDojo"` - Then, we defined a variable called `name` and assigned a value to it.
+* `echo "Hi there $name"` - Finally, we output the content of the variable on the screen as a welcome message by using `echo`.
+
+You can also add multiple variables in the file as shown below:
+
+```bash
+#!/bin/bash
+
+name="DevDojo"
+greeting="Hello"
+
+echo "$greeting $name"
+```
+
+Save the file and run it again:
+
+```bash
+./devdojo.sh
+```
+
+You would see the following output on your screen:
+
+```bash
+Hello DevDojo
+```
+Note that you don't necessarily need to add semicolon `;` at the end of each line. It works both ways, a bit like other programming language such as JavaScript!
+
+
+You can also add variables in the Command Line outside the Bash script and they can be read as parameters:
+
+```bash
+./devdojo.sh Bobby buddy!
+```
+This script takes in two parameters `Bobby`and `buddy!` separated by space. In the `devdojo.sh` file we have the following:
+
+```bash
+#!/bin/bash
+
+echo "Hello there $1"
+```
+
+`$1` is the first input (`Bobby`) in the Command Line. Similarly, there could be more inputs and they are all referenced to by the `$` sign and their respective order of input. This means that `buddy!` is referenced to using `$2`. Another useful method for reading variables is the `$@` which reads all inputs.
+
+So now let's change the `devdojo.sh` file to better understand:
+
+```bash
+#!/bin/bash
+
+echo "Hello there $1"
+
+# $1 : first parameter
+
+echo "Hello there $2"
+
+# $2 : second parameter
+
+echo "Hello there $@"
+
+# $@ : all
+```
+The output for:
+
+```bash
+./devdojo.sh Bobby buddy!
+```
+Would be the following:
+
+```bash
+Hello there Bobby
+Hello there buddy!
+Hello there Bobby buddy!
+```

ebook/en/content/005-bash-user-input.md

@@ -1,6 +1,6 @@
 # Bash User Input
 
-With the previous script, we defined a variable, and we output the value of the variable on the screen with the `echo $name`.
+With the previous script, we defined a variable, and we output the value of the variable on the screen with `echo "$name"`.
 
 Now let's go ahead and ask the user for input instead. To do that again, open the file with your favorite text editor and update the script as follows:
 
@@ -51,4 +51,4 @@ echo "Hi there $name"
 echo "Welcome to DevDojo!"
 ```
 
-Make sure to test this out yourself as well!
+Make sure to test this out yourself as well!

ebook/en/content/007-bash-arguments.md

@@ -6,7 +6,7 @@ You can pass arguments to your shell script when you execute it. To pass an argu
 ./devdojo.com your_argument
 ```
 
-In the script, we can then use `$1` in order to reference the first argument that we specified. 
+In the script, we can then use `$1` in order to reference the first argument that we specified.
 
 If we pass a second argument, it would be available as `$2` and so on.
 
@@ -71,11 +71,7 @@ For example, let's create a script that prints out the name of the file and dele
 
 echo "The name of the file is: $0 and it is going to be self-deleted."
 
-rm -f $0
+rm -f "$0"
 ```
 
 You need to be careful with the self deletion and ensure that you have your script backed up before you self-delete it.
-
-
-
-