proc redirect_variable {varname cmd} {
    rename puts ::tcl::orig::puts

    global __puts_redirect
    set __puts_redirect {}

    proc puts args {
        global __puts_redirect
        set __puts_redirect [concat $__puts_redirect [lindex $args end]]
        set args [lreplace $args end end]
        if {[lsearch -regexp $args {^-nonewline}]<0} {
            set __puts_redirect "$__puts_redirect\n"
        }
        return
    }

    uplevel $cmd

    upvar $varname destination
    set destination $__puts_redirect
    unset __puts_redirect

    rename puts {}
    rename ::tcl::orig::puts puts
}