Using Bash to display a Christmas tree

• bash
• christmas-tree

Bash, short for Bourne Again Shell, represents an improved version of Sh (Bourne Shell) and comes built-in with Linux and macOS operating systems. Serving as a shell, it furnishes a command line interface (CLI) for engaging with the computer’s operating system. This interface deciphers commands in plain text format, conveying the instructions to the operating system to execute corresponding actions.

A bash script essentially constitutes a plain text file containing a sequence of commands. These commands may include ones typically manually inputted in the shell (like ls or cd), as well as more complex commands that are usually avoided due to their intricacy. Essentially, any command accessible within the shell environment can be employed within a bash script, and vice versa.

Writing bash scripts does not require any special skills. You just write down the commands you want the computer to execute in a text file instead of individually typing them. This is handy for automating tasks, like managing files or folders. Bash scripts usually end with *.sh.

Writing the script

1. Connect to your Instance using SSH:

ssh root@<Instance Public IP>

2. Update the apt package cache and the software already installed on the Instance:

   apt update && apt upgrade -y
   

3. Create a new bash script and open it in a text editor, for example nano:

   nano xmas.sh
   

4. Copy the following bash code into the script:

   # The following line tells the shell what program to interpret the script with
   #!/bin/bash
   # tput is a command to manipulate the terminal, it can be used to change the color of text, apply effects, and generally brighten things up.
   trap "tput reset; tput cnorm; exit" 2
   clear
   tput civis
   lin=2
   col=$(($(tput cols) / 2))
   c=$((col-1))
   est=$((c-2))
   color=0
   # Set the text color to green to write the tree
   tput setaf 2; tput bold
   # Write the tree
   for ((i=1; i<40; i+=2))
   {
       tput cup $lin $col
       for ((j=1; j<=i; j++))
       {
           echo -n \*
       }
       let lin++
       let col--
   }
   ## Set the color to brown for the trunk
   tput sgr0; tput setaf 130
   # Write the Trunk in three lines
   for ((i=1; i<=3; i++))
   {
       tput cup $((lin++)) $c
       echo 'mWm'
   }
   # Write a greeting
   tput setaf 93; tput bold
   tput cup $lin $((c - 15)); echo SCALEWAY wishes you Merry christmas
   tput cup $((lin + 1)) $((c - 11)); echo And a Happy New Year 2025
   let c++
   k=1
   # Configure lights and decorations
   while true; do
       for ((i=1; i<=35; i++)) {
           # Turn off the lights
           [ $k -gt 1 ] && {
               tput setaf 2; tput bold
               tput cup ${line[$[k-1]$i]} ${column[$[k-1]$i]}; echo \*
               unset line[$[k-1]$i]; unset column[$[k-1]$i]  # Array cleanup
           }
           li=$((RANDOM % 9 + 10))
           start=$((c-li+2))
           co=$((RANDOM % (li-2) * 2 + 1 + start))
           tput setaf $color; tput bold   # Switch colors
           tput cup $li $co
           echo o
           line[$k$i]=$li
           column[$k$i]=$co
           color=$(((color+1)%8))
       }
       k=$((k % 2 + 1))
   done
   

5. Paste the copied file and press CTRL and s to save.
6. Exit nano by pressing CTRL and x.
7. Make the script executable using the chmod command (necessary because, by default, plain text files are not executable):

   chmod +x xmas.sh
   

Running the script

1. Run the script from your terminal by typing the following code:

   ./xmas.sh
   

   The script writes an animated tree on the terminal window:

   

2. Exit the script by pressing CTRL + c.