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Some useful bash snippets:

If you declare variables, use lower case names!

Using math

expr 30 + 10           # 30 + 10
expr 30 - 10           # 30 - 10
expr 30 / 10           # 30 / 10
expr 30 \* 4           # 30 x 4, needs exception!

Checking if file exists:

if [[ -f ~/.ssh/id_rsa ]]
then
        echo "id_rsa exists"
else
        echo "id_rsa does not exist"
fi

Ask for variable input:

# Read Password
echo -n Password:
read -s password
echo
# Run Command
echo $password

Ecnrypting / Decrypting file:

A useful tool for encrypting/decrypting files is ccrypt. Using this you can make use of git containing things like SSH keys:

apt-get install ccrypt -y                                  #install ccrypt
ccencrypt ~/.ssh/id_rsa*                                   #encrypt private key
ccdecrypt id_rsa.cpt -P "Enter password to decrypt file: " #decrypt private key
mv id_rsa ~/.ssh/ && chown -R user: ~/.ssh                 #move private key and set ownership
chmod 600 ~/.ssh/id_rsa                                    #set private key permissions

Install a list of programs:

progs=(
	mc
	iotop
	htop
	tmux
	wget
	ccrypt
	openssh-server
)
for program in "${progs[@]}"; do
	if ! command -v "$program" >/dev/null 2>&1; then
		apt-get install "$program" -y
	fi
done

A simple menu (ssh):

#!/bin/bash
clear

echo """

##################################################################################################
#                                                                                                #
#                               Welcome to sshmenu                                               #
#                                                                                                #
#                        Which server would you like to connect to?                              #
#                                                                                                #
#                           1) wekan (kanban)                                                    #
#                           2) wiki                                                              #
#                           3) nextcloud                                                         #
#                           4) dockervm1                                                         #
#                           5) dockertestvm                                                      #
#                                                                                                #
##################################################################################################

input number: 
"""
read -s server
echo $server
sleep 1
if [ $server = "1" ]; then
    clear
    echo "Setting up connection to wekan server..."
    sleep 2
    ssh 192.168.1.118
elif [ $server = "2" ]; then
    clear
    echo "Setting up connection to wiki server..."
    sleep 2
    ssh 192.168.1.117
elif [ $server = "3" ]; then
    clear
    echo "Setting up connection to nextcloud server..."
    sleep 2
    ssh 192.168.1.119
elif [ $server = "4" ]; then
    clear
    echo "Setting up connection to dockervm1 server..."
    sleep 2
    ssh 192.168.1.116
elif [ $server = "5" ]; then
    clear
    echo "Setting up connection to dockertestvm server..."
    sleep 2
    ssh 192.168.1.120
else
    echo "Incorrect choice, programm will now terminate..."
    sleep 3
    clear
    exit
fi
clear
exit

Conditional while loop:

if [ ! -f /usr/bin/zsh ]
then
	while true; do
		read -p "Would you like to install 'zsh'? (y/n) " yn
		case $yn in
			[Yy]* ) echo "OK, installing zsh...";
			while read program; do
				sudo apt install -y "$program"
			done <zsh
			break;;
    	    [Nn]* ) echo "ZSH will not be installed"; break;;
        	* ) echo "Please answer yes or no.";;
    	esac
	done
fi

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