Bash script to generate a mnemonic passphrase à la https://xkcd.com/936

pphrases

#!/usr/bin/env bash
##
##  generate mnemonic passphrases beginning with the given letters
##
##  Author:    Kevin Ernst
##  Date:      27 May 2021
##  License:   MIT
##  Source:    https://gist.github.com/ernstki/589bfb4adfb3869834c97bd106d58b7e
##
##  Usage:     pphrases a b c [...]
##
# shellcheck disable=SC2016

_pphrases() {
    local howmany=18
    local shuf='shuf'
    local sed='sed'

    # use 'gshuf' on macOS
    if [[ $(uname -s) == Darwin ]]; then
        shuf='gshuf'
        sed='gsed'
    fi

    for (( i=0; i<howmany; i++ )); do
        # take each input letter, 
        for l in "$@"; do
            # find one word that starts with that; omit hyphenated words and
            # words that have periods in them
            grep -i ^"$l" /usr/share/dict/words | grep -v '[-.]' | $shuf -n1
        done | $sed -n 's/\(.\)\(.*\)/\U\1\L\2/;H;${x;s/^\n//;s/\n/-/g;p;}'
        #               ^ upper-case first character, then join with dashes
    done | paste - - - | column -t 
}

_pphrases "${@}"