one of the documented procedures in this installation of the ACS
download_mkdir   dirname
What it does:
Ensures that $dirname exists. Won't cause an error if the directory is already there. Better than the stardard mkdir because it will make all the directories leading up to $dirname
Defined in: /web/philip/tcl/download-defs.tcl

Source code:

    set dir_list [split $dirname /]
    set needed_dir ""
    foreach dir $dir_list {
        if [empty_string_p $dir] {
        append needed_dir "/$dir"
        if ![file exists $needed_dir] {
            ns_mkdir $needed_dir