chainsshaw

#!/usr/bin/env bash
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Actions:   Hop through the [redacted] NAT box to SSH into [redacted] servers.
# Globals:   None.
# Options:   --key, -k, -i PRIVATE_KEY
#                Use this key for authentication (default: standard SSH key
#                locations [see man page ssh (1)]
#            --debug, -d
#                Run in debugger mode: set shell options -x and -v, and run
#                ssh in verbose mode with -vvv
# Returns:   0 for success, 1 for error.
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
chainsshaw() (
    local prog=${FUNCNAME}
    local usage=$(echo -e \
        "\nUsage: ${prog} [--key PRIVATE_KEY] [--debug] [USER@]HOST\n" \
        "\nHop through the [redacted] NAT box to SSH into [redacted] servers.")
    if ! (($#)); then
        echo -e "\n${prog}: Error: No arguments" >&2
        echo "${usage}" >&2
        return 1
    fi
    local key
    local dest
    local opt_debug
    while (($# > 0)); do
        case $1 in
            -h|--help)
                echo "${usage}"
                return
                ;;
            -d|--debug)
                opt_debug="-vvv"
                echo "================================================="
                echo "Entering debug mode"
                echo "================================================="
                set -xv
                shift 1
                ;;
            --key|-k|-i)
                if [[ ! $2 ]]; then
                    echo "chainsshaw(): Error: Missing argument for --key" \
                         "option" >&2
                    return 1
                elif [[ ! -f $2 ]]; then
                    echo "chainsshaw(): Error: \"$2\" file does not exist" >&2
                    return 1
                fi
                key=$2
                shift 2
                ;;
            *)
                if [[ ${dest} ]]; then
                    echo "chainsshaw(): Error: Too many arguments" >&2
                    return 1
                fi
                dest=$1
                shift
                ;;
        esac
    done
    local user=${dest%%@*}
    local opt_user
    if [[ ${user} ]]; then
        opt_user="-l ${user}"
    fi
    if [[ ${key} ]]; then
        ssh ${opt_debug} -i "${key}" \
            -oProxyCommand="ssh ${opt_user} -W %h:%p <hostname or IP>" \
            "${dest}"
    else
        ssh ${opt_debug} \
            -oProxyCommand="ssh ${opt_user} -W %h:%p <hostname or IP>" \
            "${dest}"
    fi
)