Conditional Execution | Introduction to Bash Scripting

HTB Content Academy
21

Thanks for the comment, I was fighting with the code for a while until I read your comment and I realized I didn’t understood the question, and I was answering something different.

1 Like
22

Hmmm… Here are my thoughts:

  1. I struggled for an hour or two on this using an ubuntu to simulate the output and it gave me one output with counter just literally echoing {1…40} and the wc output (i’m not sure why)
  2. I used a local toolbox called mobaxterm to run the code, and it ran the basic code there, and echoed everything
  3. you dont really need the if-else, because you only need the answer.

enjoy (if you can)

23

I’ve spent more time than I should on this f*cking exercise.
So, here’s my code:


#!/bin/bash

var="nef892na9s1p9asn2aJs71nIsm"

for counter in {1..5}
do
    var=$(echo -n $var | base64)
    echo $var
done

echo -n $var | wc -m

If you run that snippet, you will get up to 5 iteration and get the base64 hash for that 5th iteration along with the number of characters.
That being said. you can change 5 for 35, and you should get the right answer.
However, the answer is wrong – according to HTB.

So, I give up. Aint got time to spend more than 2 hours on this.

24

As someone mentioned in this thread, results will differ depending if you run your code from Linux, or macOS, and perhaps Windows?

image
image1920×978 112 KB

That being said. answer can be found below, you’re welcome.

#!/bin/bash

# Variable to encode
var="nef892na9s1p9asn2aJs71nIsm"

for counter in {1..40}; do
    var=$(echo $var | base64)
    
    # Check if the loop is at the 35th iteration
    if [ $counter -eq 35 ]; then
        # Print the number of characters in the variable
        echo $var | wc -c
    fi
done
1 Like
25

I had trouble creating the file and puting the content into it. I was able to figure it out through vim command.
vim filename.sh
then copy the code from the exercise script and then add if condition after var=$(echo var | base64) line

if [ counter -eq 35 ];then
count = $(echo “$var” | wc -c)
echo “$count”
fi

and make sure you have ‘done’ at the end.
Finally, hit esc and then :wq to save and exit out of the file. To execute it:
bash filename.sh

This worked for me hope it was helpful.

26

did you run this on a linux system?
I had the same problem, running it on a mac it gave a different answer than on linux. the value from linux was accepted

27

About the difference in MacOS and Linux is because of the base64 Encoding:

  • On macOS, the base64 command does not break lines by default.
  • On Linux distributions, the base64 inserts line breaks by default after 76 characters.

Can match output either by

  • base64 -b 76 on MacOS: to put line breaks after 76 chars
    OR
  • base64 -w 0 on Linux: to remove line breaks
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