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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 escape!

Checking if file exists:

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

Checking if directory exists:

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

Checking if variable equals 200

num = 200
if [[ $num -eq 200 ]]
then
        echo "$num equals 200"
else
        echo "$num does not equal 200"
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

Replace all files in a directory with empty files with the same name

#!/bin/bash

# Get the directory path
echo "Enter the path to the directory: "
read dir_path

# Check if the directory exists
if [ ! -d "$dir_path" ]; then
  echo "Error: Directory does not exist."
  exit 1
fi

# Replace all files in the directory with empty files
for file in "$dir_path"/*; do
  if [ -f "$file" ]; then
    > "$file"
  fi
done

echo "All files in the directory have been replaced with empty files."

Find SSH logins

This script assumes that you have the sshpass package installed on your system. You can install it with the following command: sudo apt-get install sshpass (for Ubuntu) or brew install http://macappstore.org/sshpass/ (for macOS).

#!/bin/bash

servers_file="servers"
users_file="users"
passwords_file="passwords"
logins_file="logins.txt"

# Check if the input files exist
if [ ! -f "$servers_file" ] || [ ! -f "$users_file" ] || [ ! -f "$passwords_file" ]; then
  echo "Error: One or more of the input files do not exist."
  exit 1
fi

# Read the servers, users, and passwords into arrays
servers=($(cat "$servers_file"))
users=($(cat "$users_file"))
passwords=($(cat "$passwords_file"))

# Loop through all combinations of servers, users, and passwords
for server in "${servers[@]}"; do
  for user in "${users[@]}"; do
    for password in "${passwords[@]}"; do
      # Try to ssh into the server with the current combination of user and password
      ssh_output=$(sshpass -p "$password" ssh "$user"@"$server" -o StrictHostKeyChecking=no -o ConnectTimeout=3 2>&1)

      # Check if the ssh login was successful
      if [ "$?" -eq 0 ]; then
        echo "Successful ssh login to $server using account $user and password $password"
        echo "$server $user $password" >> "$logins_file"
      else
        echo "Failed ssh login to $server using account $user and password $password"
      fi
    done
  done
done

Verhaar_Wiki

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