functions

...
function getEnv {
        ${1:+\:} return 1
        typeset -n name ret=$1
        typeset -a names
        compgen -e | mapfile -t names
        set -- "${names[@]}"
        for name; do
                ret[${!name}]=$name
        done
}
...

functions-tmux

...
set +o posix
shopt -s extglob lastpipe

function main {
        typeset myRootPath
        if myRootPath=$(dirname "$(readlink -snf -- "$BASH_SOURCE")") && [[ -d $myRootPath ]]; then
                source "${myRootPath}/functions" || return
                unset -f main
        else
                return 1
        fi
}

main

function tmuxUpdateGlobalEnv {
        [[ $(type -t getEnv) == function && $TMUX ]] || return
        [[ ${EUID:-$(id -u)} == 0 ]] && env-update
        (
                exec -c -- bash -O lastpipe -O extglob /dev/fd/3 "$(typeset -fp getEnv)" "$TMUX"
        ) 3<<-'EOF'
        source /etc/profile
        eval -- "$1" || exit
        typeset -A _myEnv
        getEnv _myEnv || exit
        typeset _key
        for _key in "${!_myEnv[@]}"; do
                TMUX=$2 tmux setenv -g "$_key" "${_myEnv[$_key]}"
        done
EOF
}
...

tmux.conf

set-hook -g client-attached \
        'run-shell -b "{ source ~ormaaj/doc/projects/dotfiles/common/home/shell/functions-tmux.ksh; tmuxupdateglobalenv; } 2>&1"'

bind -T prefix y if-shell -b \
        'set -o pipefail && for _ in DISPLAY XAUTHORITY; do eval "$(tmux showenv -st #{session_id} "$_")"; done && tmux saveb - | xsel -d "${DISPLAY:-:0}" -i' \
        'display "Sent tmux buffer to primary X selection."' \
        'display "Failed setting selection."'

bind -T prefix C-p if-shell -b \
        'set -o pipefail && for _ in DISPLAY XAUTHORITY; do eval "$(tmux showenv -st #{session_id} "$_")"; done && xsel -d "${DISPLAY:-:0}" -o | tmux loadb -' \
        'display "Sent tmux buffer to primary X selection."' \
        'display "Failed loading selection."'