Bash scripts examples

project introduction

This project looks at various tasks that can be accomplished using bash scripting.
Most of the examples are taken from the course exercises of Mastering Linux: The Comprehensive Guide.
The database backup script, db-backup-script.sh, is one I use to backup my personal database.

Bash Scripts:

1. bulk-image-downloader.sh

   This script loops through using a counter and downloads images using curl from a specified url.
   The script breaks out of the loop when the number of "notfound" images reaches 10.

   curl --fail "${url/\%\%/$counter}" -o "image-${counter}.jpg"
   

2. city-weather.sh

   This script prompts the user for a City name and then sends a request to a weather API
   to fetch the current temperature in degrees Celsius.
   The temperature is then converted to Fahrenheit.
   Both temperatures are then displayed back to the user.

   curl 'https://downloads.codingcoursestv.eu/055%20-%20bash/api/api.php' -G --data-urlencode "city=${city}" -o "${city_no_blanks}_data.json" -L -s
   

3. db-backup-script.sh

   This script takes a backup of the database. It pulls in database credentials from environment variables.
   Then finally removes backups older than 15 days.

   mysqldump -u$DB_USER_1 -p$DB_PASSWORD_1 $DB_NAME_1 > ${BACKUP_DIR_1}${DB_NAME_1}-${BACK_UP_1}-${TIMESTAMP}.sql
   find $BACKUP_DIR -type f -name "*.sql" -mtime +15 -exec rm {} \;
   

4. dialog-input-box.sh

   This script prompts the user for a name using a dialog box.
   The name is then appended to a text file and the user is
   presented options to either enter the next name or quit.
   Finally, the text file is printed on screen.

   name=$(dialog --keep-tite --title 'Important input' --backtitle 'Course signup'  --inputbox 'Please enter the name: ' 0 0 2>&1 >/dev/tty)
   

   Note, dialog has to be pre-installed for this to work

   sudo apt-get update && sudo apt-get install dialog
   or
   dnf install dialog
   

5. directory-monitor.sh

   This script allows us to easily monitor the size of directories The directories are passed in as arguments to the script Then for each of those directories, we want to:

   • Calculate the total size of the directory (with the du program)
   • Then, check if this size is above a defined threshold (5 megabytes)
   • If this is the case, we want to print out the size of this directory

   read -r size rest < <(du -sm "${folder}")
   

   Invoking the script with arguments:

   ./directory-monitoring.sh -d Krausen-and-Maentz -d iptables-terraform -d Practice
   

6. download-file.sh

   This script downloads and analyzes an eBook and outputs the finding on screen.
   The tasks include:
   

   • Downloads eBook file - but only when needed!
     i.e. if the file doesn't exist in a specified directory
   • And then, calculates how many lines contain the word "love" atleast 1 time
     i. It should print error messages to stderr
     ii. Example of printing to stderr
     

     echo 'I am an error message' >&2
     

     iii. It should exit with the correct exit code on error
     i.e. if an error occurs then a non-zero exit code should be set
     This can be done with a file that sets an exit code

   curl https://downloads.codingcoursestv.eu/055%20-%20bash/if/romeo.txt -o romeo.txt -s
   

7. image-thumbnail-processor.sh

   This script processes all images in a directory:
   Checks if a thumbnail already exists, If it does, skip generating a new thumbnail
   check, if it needs to generate a thumbnail at all
   (meaning that width / height of the image is greater than 100 pixels)
   Only then, a thumbnail should be generated.

   width=$(identify -format '%w' "${filename}")
   height=$(identify -format '%h' "${filename}")
   
   convert "${filename}" -resize 100x100 "${thumbnail_filename}"
   

8. trivia-quiz.sh

   This script creates a function load_question
   When invoked, load_question should load the trivia.json file,
   determine how many questions are in it, and provide a random question
   Example:
   What did the first moving picture depict?

   • A galloping horse (correct response)
   • A woman in a dress
   • A man walking
   • A crackling fire

   Note jq must be installed prior to running the script

   sudo apt-get update && sudo apt-get install jq