proc du { args } {
    switch -exact [llength $args] {
        0 {
            set dir .
            set switch -k
        }
        1 {
            set dir $args
            set switch -k
        }
        2 {
            set switch [lindex $args 0]
            set dir [lindex $args 1]
        }
        default {
            set msg "only one switch and one dir "
            append msg "currently supported"
            return -code error $msg
        }
    }

    set switch [string tolower $switch]

    set -b 1
    set -k 1024
    set -m [expr 1024*1024]

    set result [list]

    if {![file isdirectory $dir]} {
        set ary($dir,bytes) [file size $dir]
        set globpats [list]
    } else {
        set globpats $dir/*
    }

    while {[llength $globpats]} {
        foreach globpat $globpats {
            set cwd [string trim $globpat */]
            set ary($cwd,bytes) 0
            set files [glob -nocomplain $globpat]
            set globpats [list]
            foreach file $files {
                if {![catch {
                    file readlink $file
                }]} {
                    continue
                }
                if {[file isdirectory $file]} {
                    lappend globpats $file/*
                } else {
                    incr ary($cwd,bytes) [file size $file]
                }
            }
        }
    }

    set dirs [array names ary]

    # Since the directories are arranged by nesting level,
    # this can be optimised to not iterate in the inner loop
    # over directories already processed by the outer loop.
    # I have no time right now...
    if {[llength $dirs] > 1} {
        foreach dir $dirs {
            set dir [lindex [split $dir ","] 0]
            foreach Dir $dirs {
                set Dir [lindex [split $Dir ","] 0]
                if { [string match $dir/* $Dir]} {
                    incr ary($dir,bytes) $ary($Dir,bytes)
                }
            }
        }
    }

    foreach dir $dirs {
        set name [lindex [split $dir ","] 0]
        set size [expr {$ary($dir) / [set $switch]}]
        lappend retval [list $name $size]
    }
    # copyright 2002 by The LIGO Laboratory
    return $retval
}

# Test:
catch {console show}
catch {wm withdraw .}

puts "disc usage - start at current directory:"
puts "[du]"

puts "Test2 - show result as one long line:"
set  tx [du ..]
puts $tx

puts "Test3 - show result as one dir per line, size in MB:"
set  tx [du -m C://WINNT]
foreach dir $tx {puts "$dir"}
#.

    set things {1 2 3}

    while {[llength $things]} {
        puts "Entered 'while' loop ([join $things])"
        foreach thing $things {
            puts "Entered 'foreach' loop ($thing : [join $things])"
            set things [list]
    
            if {$thing == 2} {
                lappend things a
            }
        }
    }