Code:

 proc {commas} {var {num 3} {char ","}} {    set len   [string length $var]    set first [expr $len - $num]    set x     ""    while { $len > 0} {# grab left num charsset lef [string range $var $first end]if {[string length $x] > 0} {    set x   "${lef}$char${x}"} else {    set x   ${lef}}# grab everything except left num charsset var [string range  $var 0 [expr $first -1]]set len   [string length $var]set first [expr $len - $num]    }    return $x }