Shell usage is the most important skill of a Linux user, which is why we first introduced the concept during week 2. So far, we used bash interactively, by typing commands one after another. Often, it makes sense to execute a chain of commands automatically. Remember how repetitive it was to conduct arpspoof attacks? Actions can be automated with scripts. A basic introduction to bash syntax is available on our wiki. Below is an example of a pointless script. It does not take full advantage of bash’s many features, so that the syntax would be easier to understand.
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#!/bin/bash
if [[ "$1" = *"-h"* ]]; then
cat << EOF
usage: ./example.sh [OPTION]
optional arguments:
-h, --help show this help message and exit
--create-folder make a folder
EOF
exit 0
elif [ "$1" = "--create-folder" ]; then
folder_name=tux_the_penguin
mkdir $folder_name
echo "Made a folder, it's name is \"$folder_name\""
printf "Should I remove that folder now? [y/N] " # no new line
read response
if [ "$response" = "y" ] || [ "$response" = "Y" ] || [ "${response,,}" = "yes" ]; then
rmdir $folder_name
echo "I removed the folder."
fi
fi
echo "Goodbye"
Steganography (potato followup)
You can review the solution here. https://github.com/twlinux/potato/wiki
It’s your turn! Write a bash script which appends plaintext to image files. Below is sample output.
$ ./hide.sh image.jpg
Enter secret text: chicken nugger and french fried
$ ./hide.sh --reveal image.jpg
The secret is: chicken nugger and french fried
Feel free to add more features, the most impressive script will win the sticker below.
