     trap [ arg ] [ sig ] ...
          arg is a command to be read and executed when the shell
          receives  sig.  Each sig can be given as a number or as
          the name of a signal.  If arg is -, then all traps  sig
          are  reset to their default values.  If arg is the null
          string, then this signal is ignored by the shell and by
          the  commands  it invokes.  If sig is ERR then arg will
          be executed after each command.  If sig is  0  or  EXIT
          and the trap statement is executed inside the body of a
          function, then the command arg is  executed  after  the
          function  completes.   If sig is 0 or EXIT and the trap
          statement is not executed inside the body  of  a  func-
          tion,  then  the command arg is executed when the shell
          terminates.  The trap command with no arguments  prints
          a list of commands associated with each signal.
