Commify

proc _commify {num {sep ,}} {
  # commify --
  #   puts commas into a decimal number
  # Arguments:
  #   num		number in acceptable decimal format
  #   sep		separator char (defaults to English format ",")
  # Returns:
  #   number with commas in the appropriate place
  #
 
  while {[regsub {^([-+]?\d+)(\d\d\d)} $num "\\1$sep\\2" num]} {}
  return $num
}