create_passphrase.sh

#!/bin/bash

num_words="$1"
orig_dict="$2"
dict_file=''
ret_value=0

max_word_len=9 # Exclude words longer than this
phrase_count=6 # How many passphrases to generate

(( num_words > 0 )) || (( num_words = 4 ))

[[ "$orig_dict" ]] || {
  for sfx in '-small' '' '-large' '-huge' '-insane'; do
    orig_dict="/usr/share/dict/american-english$sfx"
    [[ ! -e "$orig_dict" ]] || break
    orig_dict="/usr/share/dict/british-english$sfx"
    [[ ! -e "$orig_dict" ]] || break
  done
}

[[ -e "$orig_dict" ]] || {
  echo 'No dictionary found' >&2
  exit 1
}

dict_file="$(mktemp -p /dev/shm tmp-dict.XXXXXXXX)"
LANG=C egrep "^[[:alpha:]]{1,$((max_word_len))}$" "$orig_dict" > "$dict_file"

dict_size=$(wc -l "$dict_file" 2>/dev/null | cut -d' ' -f1)
if (( dict_size < 1 )); then
  echo 'Empty dictionary' >&2
  ret_value=1
else
  if [[ -t 2 ]]; then
    B='\e[32m'; L='\e[34m'; E='\e[33m'; R='\e[36m'; N='\e[0m'
  else
    B=''; L=''; E=''; R=''; N=''
  fi

  echo -e "$B[${L}num_words$E=$R$num_words$B]$N" >&2
  echo -e "$B[${L}dict_size$E=$R$dict_size$B]$N" >&2
  echo -e "$B[${L}entropy$E=$R$(bc -l <<< "scale=3; l($dict_size^$num_words)/l(2)")$B]$N" >&2

  rand_mask='0xffffffff'

  while (( rand_mask >= dict_size )); do
    (( m = rand_mask >> 1 ))
    (( m >= dict_size )) || break
    rand_mask=$(printf '0x%x\n' "$m")
  done

  for (( i = 0; i < 6; i++ )); do
    (( n = num_words ))
    while (( n > 0 )); do
      R=$(od -N4 -tu4 -An -w4 /dev/urandom | tr -d ' ')
      R=$((R & rand_mask))
      (( R < dict_size )) || continue
      W=$(tail -n+$((R+1)) "$dict_file" | head -1)
      W="$(tr '[:lower:]' '[:upper:]' <<< ${W:0:1})${W:1}"
      echo -n "$W"
      (( n-- ))
    done
    echo
  done
fi

rm -f "$dict_file"

exit $ret_value