Use Bash to display a Christmas tree

Bash Scripting - Overview

Bash (Bourne again shell) is an improved version of Sh (Bourne shell) and is available by default on Linux and MacOS operating systems. A shell provides a command line interface (CLI) to interact with the operating system of a computer. It interprets commands in plain text format and passes the information to the operating stems to launch an action.

A Bash script is a plain text file containing a series of commands. These commands can be a mixture of commands you would normally type by yourself on the shell (like ls or cd) and other commands you would normally not type by yourself as they can be more complex. Any command available on the shell can be used in a bash script - and vice versa.

No special knowledge is required to write bash scripts, as they are plain text files containing the series of commands required to run a specific task. Instead of typing then manually on the shell, you write them in a script and run the script afterwards. This can be very useful for system administration tasks as you can automatize tasks. The common file extension for bash scripts is *.sh.

Getting Started

1 . Connect to your instance using SSH

2 . Update the apt packet 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 content 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 2020
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 . Write the file by pressing CTRL and o and exit nano by pressing CTRL and x.

6 . By default plain text files are not executable. Make the script Executable using the chmod command:

chmod +x xmas.sh

Running the Script

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

./xmas.sh

2 . The script writes an animated tree on the terminal window:

3 . Exit the script by pressing CTRL + c.