Bash Scripting
This post introduces the basics of Bash scripting, including how to comment code, declare variables, accept arguments, use arrays and apply conditionals. It includes hands-on examples and explanations.
Difficulty: Easy
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Note: This write-up is a concise guide meant to complement the TryHackMe Bash Scripting room. It is not a comprehensive theoretical resource but rather a practical walkthrough of key concepts and tasks. For deeper explanations, refer to the room materials or other Bash documentation.
Room Setup
Use the TryHackMe AttackBox or your own terminal.
🧩 Tasks Breakdown
Task 2
❓ What piece of code can we insert at the start of a line to comment out our code?
Answer: #
Explanation: Bash ignores everything written on the line after the hash mark (#), but as for every rule there is an exception, the exception here is when the first line of the script starts with the #! characters (the so-called Shebang). The Shebang is what tells the operating system which interpreter to use to parse the rest of the file.
❓ What will the following script output to the screen, echo “BishBashBosh”
Answer: BishBashBosh
Explanation: echo does exactly what it promises, it echoes your words back! 
Task 3
❓ What would this code return?
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name="Jammy"
age=21
echo "$name is $age years old"
city="Paris"
country="France"
Answer: Jammy is 21 years old
Explanation: This code assigns values to four variables (name=“Jammy”, age=21, city=“Paris” and country=“France”). The only visible action is the echo command, which uses the name and age variables. When we run the script, these variables get replaced with their values and so we get that Jammy is 21 years old.
❓ How would you print out the city to the screen?
Answer: echo $city
Explanation: Remember that the echo command behaves very similarly to the print function in Python.
❓ How would you print out the country to the screen?
Answer: echo $country
Explanation: Exactly the same line of thought as the question above :)
Task 4
Check out the Bonus section for some examples of the scripts they encouraged us to experiment with!
❓ How can we get the number of arguments supplied to a script?
Answer: $#
Explanation: Think of # as short for “how many”, so $# gives us the total number of arguments passed to the script (the script name is not included). Friendly reminder: if you are only using read and nothing was passed when running the script, $# will be 0, as it only counts arguments passed at runtime, not interactive input collected inside the script. As an example, if you were to count the number of arguments supplied to script 1, you would get 3, but if you were to do the same thing for script 2, you would get 0.
❓ How can we get the filename of our current script(aka our first argument)?
Answer: $0
Explanation: $0 is the way and regarding its format, I found this discussion very interesting.
❓ How can we get the 4th argument supplied to the script?
Answer: $4
Explanation: Example: with ./some_script.sh parameters can seem complicated, the 4th argument would be “complicated” (wink wink)
❓ If a script asks us for input how can we direct our input into a variable called ‘test’ using “read”
Answer: read test
Explanation: Check the read manual.
❓ What will the output of “echo $1 $3” if the script was ran with “./script.sh hello hola aloha”
Answer: hello aloha
Explanation: $1 and $3 refer to the first and third arguments passed to the script, in that order. Here, that means “hello” and “aloha”.
Task 5
cars=('honda' 'audi' 'bmw' 'tesla')
❓ What would be the command to print audi to the screen using indexing.
Answer: echo "${cars[1]}"
Explanation: In Bash, arrays are zero-indexed. cars[0] = "honda", cars[1] = "audi", cars[2] = "bmw", cars[3] = "tesla"
❓ If we wanted to remove tesla from the array how would we do so?
Answer: unset cars[3]
Explanation: Removing an item from an array is done with unset.
❓ How could we insert a new value called toyota to replace tesla?
Answer: cars[3]='toyota'
Explanation: To change an item in the cars array at a specific position, we use cars[index]='value'.
Task 6
❓ What is the flag to check if we have read access to a file?
Answer: -r
Explanation: See this list of flags and their uses.
❓ What is the flag to check to see if it’s a directory?
Answer: -d
Explanation: Check link above.
Bonus
Code Snippet 1
A little biography maker that takes name, age and job as parameters when you run the script, stores them in variables and prints the bio.
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#!/bin/bash
name=$1
age=$2
job=$3
echo "Hi, I'm $1, I'm $2 and I'm a $3! :)"
Code Snippet 2
Same idea as the one above, but interactive.
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#!/bin/bash
echo Enter your name
read name
echo Enter your age
read age
echo Enter you job
read job
echo "Hi, I'm $name, I'm $age and I'm a $job! :)"
Code Snippet 3
Upgrading Code Snippet 1 by introducing arrays. Now it loops through multiple people, storing names, ages and jobs in arrays and printing the bio for each one.
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#!/bin/bash
names=('Bianca' 'Mohammed' 'Yan' 'Maria')
age=(21 17 34 25)
job=('System Dev Engineer' 'Student' 'Cook' 'Data Scientist')
for index in ${!names[@]}; do
echo "Hi, I'm ${names[$index]}, I'm ${age[$index]} and I'm a ${job[$index]}! :)"
done
Code Snippet 4
Building on top of Code Snippet 2, this script uses an if/else statement to check the user’s age. If the age is under 18, it prints a message saying the user is not eligible for work. If the age is 18 or over, it asks for their job and prints a personalized message.
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#!/bin/bash
echo Enter your name
read name
echo Enter your age
read age
if [ $age -lt 18 ]
then
echo "$name, you are not eligible for work!"
else
echo Enter your job
read job
echo "Hi $name, we have a vacancy for the position of $job! :)"
fi
Confusion.log
💭 Bash is a scripting language, what other languages are there?
Answer: Besides Bash, other notable scripting languages include AWK, Groovy, Windows PowerShell, etc. You can check out a fuller list here.
💭 To .sh or Not to .sh?
Answer: When I was creating the first script, I just named it biography. No extension. No second thoughts. Then I looked around the [TryHackMe :p] room and noticed that all files were in the format file.sh and I thought “waaaaaait… why is my script working then?”. There’s a really nice Reddit thread that answers this , but here’s the TL;DR: the file extension doesn’t matter to the shell. As long as there is a valid Shebang line at the top (such as #!/bin/bash)!!! Using .sh is a convention, not a requirement. It helps humans know it’s a shell script. Unix-like systems (Linux, macOS) don’t use file extensions to determine how to run a file (unlike Windows).
Bumps and Bruises
❗️ Never leave a space between the variable name, the ”=” and the value.
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# WRONG:
name = "John"
# RIGHT:
name="John"
❗️ Never forget to give running permissions to your script.
chmod +x your_script.sh
❗️ Quoting variables when echoing or using them avoids surprises with spaces or special characters.
echo "$name"
