Generate random passphrase on OSX with bash

gen_passphrase.sh

#!/bin/bash
# Only tested on OSX
DICT="/usr/share/dict/words"
CEIL=$(wc -l "$DICT" | tr -s '[:blank:]' ' ' | cut -d' ' -f2)

if [ "$#" -lt 1 ] ; then
    LEN="5"
else
    LEN="$1"
fi

i=0
while [ "$i" -lt "$LEN" ] ; do
    RN=$(dd if=/dev/urandom count=4 bs=1 2>/dev/null | od -t u  | head -n1 | tr -s '[:blank:]' ' ' |   cut -f 2 -d' ')
    IDX=$(((RN % CEIL) + 1))
    sed "${IDX}q;d" "$DICT"
    i=$((i+1))
done | xargs echo