Generate strong password of any given width from any given text or master password

passgen.bash

#!/usr/bin/env bash
# Creates strong password of any given width from any given text or master password
# Usage: echo <a line of text> | [SALT=<salt>] ./passgen [-p] [<width>]
# Option: -p generates PIN instead of password
# Default: width=8; SALT=somesalt
# Author: Somajit Dey <dey.somajit@gmail.com>
# License: GNU GPLv2

set -o noglob

hash_salt(){
  salt="$(echo "${salt}" | sha512sum | awk '{print $1}')"
}; export -f hash_salt

test_format(){
  [[ "${string}" =~ [a-z]+ ]] && [[ "${string}" =~ [A-Z]+ ]] && \
  [[ "${string}" =~ [0-9]+ ]] && [[ "${string}" =~ [^a-z^A-Z^0-9]+ ]]
}; export -f test_format

getopts p option
case "${option}" in
p)
  export pin_mode="true"
  list=({0..9})
  ;;
*)
  export pin_mode="false"
  list=({A..Z} {a..z} {0..9})
special_chars=\
('!' '@' '#' '$' '%' '^' '&' '*' '(' ')' '_' '-' '+' '=' '{' '}' '[' ']' '|' '\' ';' ':' "'" '"' ',' '.' '/' '?' '~' '`')
  list+=(${special_chars[@]})
  ;;
esac
base=${#list[@]}

width="${!OPTIND:-8}"
if ! "${pin_mode}"; then ((width<4)) && echo "Desired password width must be >=4" >&2 && exit 1;fi
read -re mpasswd # Master-password
salt="${SALT:-somesalt}_${width}"

until test_format; do
  string=
  hash_salt

  hex=$(python3 -c "import hashlib; print(hashlib.pbkdf2_hmac('sha512', b'${mpasswd}', b'${salt}', 100000, ${width}).hex())")

  for i in $(echo "${hex}" | fold -w 2);do
    index=$((16#$i % $base))
    string="${string}${list[$index]}"
  done

  salt="${salt}_${string}"

  "${pin_mode}" && break
done

echo "${string}"