purge_user.sh

#!/bin/bash
# Disclaimer: my first bash script
# User purger - removes the user and their public keys from a system
# By chendo

if [ "$(id -u)" != "0" ]; then
   echo "This script must be run as root" 1>&2
   exit 1
fi

read -p "Enter username to be deleted (or leave blank to delete key): " target_user
if [ "$target_user" == "" ]; then
  read -p "Enter part of public key (must be more than 10 characters): " key
  if [ test $(expr length "$key") -lt 10 ]; then
    echo "Less than 10 characters, bailing"
    exit 1
  fi
  output=$(
    for f in `cut -d : -f 6 /etc/passwd`; do
      grep -nHs "$key" $f/.ssh/authorized_keys
    done
  )  
else
  home_folder=( $(grep $target_user /etc/passwd | cut -d : -f 6))
  keys="$home_folder/.ssh/authorized_keys"
  output=$(while read key; do
    
    if [[ $key =~ ^.{,10}$ ]]; then
      continue
    fi
    for f in `cut -d : -f 6 /etc/passwd`; do
      grep -nHs "$key" $f/.ssh/authorized_keys
    done
  done < "$keys" )

fi

while read line; do
  filename=$(echo "$line" | cut -d : -f 1)
  line_no=$(echo "$line" | cut -d : -f 2)
  if [ $filename ]; then
    echo "$line"
  fi
done < <(echo "$output")


read -p "Are you sure you want to delete these instances of the public keys? (yes/no) " confirm
if [ "$confirm" == "yes" ]; then
  while read line; do
    filename=$(echo "$line" | cut -d : -f 1)
    line_no=$(echo "$line" | cut -d : -f 2)
    if [ $filename ]; then
      sed -i ${line_no}d "$filename"
    fi
  done < <(echo "$output")
fi

if [[ $target_user =~ ^.+$ ]]; then
  read -p "Are you sure you want to delete the user? (yes/no) " confirm
  if [ "$confirm" == "yes" ]; then
    deluser $target_user
  fi
fi