pwgen-word

#!/bin/bash
set -eu
set -o pipefail

default_opts="-sy"

usage() {
    cat >&2 <<EOM
usage: $(basename "$0") [-v] LENGTH [PWGEN_OPTS...]

Generate random passwords using pwgen that have no punctuation characters that
gnome-terminal considers to be word separators.

It sends pwgen a length that is 25% larger than LENGTH to get enough data.

If PWGEN_OPTS are given, they will be passed to pwgen. Otherwise, default
options of "$default_opts" will be used.

Punctuation according to gnome-terminal:
    word separators: !"$'()*;<>[\\]^\`{|}
    non separators:  #%&+,-./:=?@_~

Caveat: The word separators have recently changed quite a bit.
        https://askubuntu.com/a/725109/8807
        https://bugs.launchpad.net/ubuntu/+source/gnome-terminal/+bug/1401207

There are 14 non-separators, so with default options there are 76 possible
symbols. Generated passwords will have somewhat less than 6.248 bits of entropy
per character because each one of symbols, uppercase, lowercase, and numbers
are required to be present by default.

OPTIONS
    -v      Be more verbose.

SEE ALSO
    pwgen(1)
EOM
    exit 1
}

log() {
    test -n "$verbose" || return 0
    echo >&2 "$*"
}

verbose=
if [ $# -ge 1 ] && [ "$1" = "-v" ]; then
    verbose=1
    shift
fi

if [ $# -lt 1 ]; then
    usage
fi

target="$(printf "%d" "$1")"
shift

pwlen="$((target * 5 / 4))"

pwopts="$*"
if [ -z "$pwopts" ]; then
    pwopts="$default_opts"
fi

while true; do
    log "+ pwgen $pwopts $pwlen | tr -d "'!"$'\''()*;<>[\\]^`{|}'
    pass="$(pwgen $pwopts "$pwlen" | tr -d '!"$'\''()*;<>[\\]^`{|}')"
    len="${#pass}"

    if [ "$len" -gt "$target" ]; then
        log "len: $target (truncated from $len)"
        pass="${pass:0:$target}"
        break
    elif [ "$len" -eq "$target" ]; then
        log "len: $len"
        break
    else
        log "len: $len"
    fi
done

echo "$pass"