test-passwd-match.sh

#!/usr/bin/env bash

function cat_passwd_column() {
    awk -F: '{ print $2; }'
}

function cat_passwd_salt() {
    awk -F'$' '{ print $3; }'
}

function get_shadow() {
    local USERNAME="$1"

    getent shadow "$USERNAME"
}

USERNAME="$1"
PASSWORD="$2"

get_shadow "$USERNAME" | cat_passwd_column
echo -n "$PASSWORD" | openssl passwd -1 -stdin -salt "$(get_shadow "$USERNAME"  | cat_passwd_column | cat_passwd_salt)"