passgen.sh

#!/bin/bash
#Author: Joshua Kroger
#https://github.com/ProbieK/

#Set Default Values
silent='false'
GUI='false'
char='graph'
engine='perl'
num_min='16'
num_max='24'

#Detect OS for later special uses
#(coming soon: native bash on WSL support)
if [ "$(uname)" == "Darwin" ]; then
    HOSTOS='MACOS'
elif [ "$(expr substr $(uname -s) 1 5)" == "Linux" ]; then
    HOSTOS='LINUX'
elif [ "$(expr substr $(uname -s) 1 10)" == "MINGW32_NT" ]; then
    HOSTOS='WIN32'
elif [ "$(expr substr $(uname -s) 1 10)" == "MINGW64_NT" ]; then
    HOSTOS='WIN64'
fi

#Detect if script is running in a GUI or not
if [ "$DISPLAY" ]; then
    GUI='true'
fi

#Do help stuff
function show_help {
    echo ""
    echo "Usage:"
    echo "$ ./passgen.sh [option] [value]"
    echo "You may call the script without flags and it will generate a password"
    echo "between 16 and 24 characters long in the \"graph\" character set."
    echo ""
    echo "Example:"
    echo "$ ./passgen.sh"
    echo "or"
    echo "$ ./passgen.sh -n 16"
    echo "or"
    echo "$ ./passgen.sh -n 16 -c graph"
    echo ""
    echo "Sample Output:"
    echo "Password Length:  16"
    echo "Password Charset: graph"
    echo "@hA}x8GQtNJ6u_)0"
    echo ""
    echo "Command Line Options:"
    echo "-h or --help      Shows this help and exits"
    echo "-n or --number    Modifies the length of the password"
    echo "-c or --char      Modifies the character set"
    echo "-s or --silent    Silences all optional terminal output"
    echo "-m or --min       Sets the minimum length of the password (must be used with --max or unexpected lengths will result)"
    echo "-x or --max       Sets the maximum length of the password"
    echo "-g or --grep      Uses grep as the engine to select random characters"
    echo "-p or --perl      Uses perl as the engine to select random characters"
    echo "(perl is the defualt engine)"
    echo ""
    echo "Charactor Set Options:"
    echo 'digit		Digits: 0-9'
    echo 'lower		Lower-case letters: a-z'
    echo 'upper		Upper-case letters: A-Z'
    echo 'alpha		Alphabetic characters: lower and upper: A-Za-z'
    echo 'alnum		Alphanumeric characters: alpha and digit: 0-9A-Za-z'
    echo 'punct		Punctuation characters'
    echo 'graph		Graphical characters: alnum and punct'
    echo 'print		Printable characters: alnum, punct, and space'
    echo ''
    exit 0
}

function set_min_max {
    num=$(awk -v min=$num_min -v max=$num_max 'BEGIN{srand(); print int(min+rand()*(max-min+1))}')
}

#Parse Command Line Options
ARGS=( "$@" )
for i in "${!ARGS[@]}"; do
    case "${ARGS[i]}" in
        '')
            continue
            ;;
        -h|--help)
            show_help
            ;;
        -g|--grep)
            num="${ARGS[i+1]}"
            engine='grep'
            unset 'ARGS[i+1]'
            ;;
        -p|--perl)
            num="${ARGS[i+1]}"
            engine='perl'
            unset 'ARGS[i+1]'
            ;;
        -n|--number)
            num="${ARGS[i+1]}"
            num_flag='1'
            unset 'ARGS[i+1]'
            ;;
        -c|--char)
            char="${ARGS[i+1]}"
            unset 'ARGS[i+1]'
            ;;
        -s|--silent)
            silent='true'
            ;;
        -m|--min)
            num_min="${ARGS[i+1]}"
            num_min_flag='1'
            unset 'ARGS[i+1]'
            ;;
        -x|--max)
            num_max="${ARGS[i+1]}"
            num_max_flag='1'
            unset 'ARGS[i+1]'
            ;;
        --)
            unset 'ARGS[i]'
            break
            ;;
        *)
            continue
            ;;
    esac
        unset 'ARGS[i]'
done

#Error Checking
charsets=( digit lower upper alpha alnum punct graph print )
if [[ ! " ${charsets[@]} " =~ " $char " ]]; then
    echo "Charset not recognized! Aborting!"
    exit 1
fi
if [ "$num_min_flag" == '1' ]; then
    if [ ! "$num_max_flag" == '1' ]; then
        echo "When you set a minimum number, a maximum must also be used."
        echo "Aborting!"
        exit 1
    fi
fi
if [ "$num_max_flag" == '1' ]; then
    if [ ! "$num_min_flag" == '1' ]; then
        echo "When you set a maximum number, a minimum must also be used."
        echo "Aborting!"
        exit 1
    fi
fi

#Set min and max length values if it wasn't explicitly defined
if [ ! "$num_flag" == '1' ]; then
    set_min_max
fi

#Password Stats
if [ $silent == "false" ]; then
    echo "Password Length:  $num"
    echo "Password Charset: $char"
fi

#The meat and potatos of this password generator
if [ "$engine" == "grep" ]; then
  var=$(strings - /dev/urandom | grep -o "[[:"$char":]]" | head -n "$num" | tr -d '\n')
elif [ "$engine" == "perl" ]; then
  var=$(strings - /dev/urandom | perl -p -e "s/[^[:"$char":]]//g" | head -c "$num" | tr -d '\n' )
else
  echo "No engine selected! How did you manage that?"
  echo "Exiting"
  exit 0
fi
echo "Engine: $engine"
printf '\033[0;36m%s\033[0m\n' "$var"

#Copy password to clipboard on MacOS
if [ $HOSTOS == "MACOS" ]; then
    printf '%s' "$var" | pbcopy
fi

#Copy password to clipboard on Linux hosts with xclip
if [ $HOSTOS == "LINUX" ]; then
    if command -v xclip > /dev/null; then
        if [ $GUI == "true" ]; then
            printf '%s' "$var" | xclip -selection c
        fi
    else
        if [ $silent == "false" ]; then
            echo "If you install xclip, I can copy the password right to your clipboard!"
        fi
    fi
fi