trap [ arg ] [ sig ... ]
       arg is a series of commands (usually quoted to protect it from
       immediate evaluation by the shell) to be read and executed when
       the shell receives any of the signals specified by one or more sig
       args.  Each sig can be given as a number, or as the name of a
       signal either with or without the string SIG in front (e.g. 1,
       HUP, and SIGHUP are all the same signal).

       If arg is `-', then the specified signals are reset to their
       defaults, or, if no sig args are present, all traps are reset.

       If arg is an empty string, then the specified signals are ignored
       by the shell (and by the commands it invokes).

       If arg is omitted but one or more sig args are provided (i.e.  the
       first argument is a valid signal number or name), the effect is
       the same as if arg had been specified as `-'.

       The trap command with no arguments prints a list of commands
       associated with each signal.

       If sig is ZERR then arg will be executed after each command with a
       nonzero exit status.  ERR is an alias for ZERR on systems that
       have no SIGERR signal (this is the usual case).

       If sig is DEBUG then arg will be executed before each command if
       the option DEBUG_BEFORE_CMD is set (as it is by default), else
       after each command.  Here, a `command' is what is described as a
       `sublist' in the shell grammar, see the section SIMPLE COMMANDS &
       PIPELINES in zshmisc(1).  If DEBUG_BEFORE_CMD is set various
       additional features are available.  First, it is possible to skip
       the next command by setting the option ERR_EXIT; see the
       description of the ERR_EXIT option in zshoptions(1).  Also, the
       shell parameter ZSH_DEBUG_CMD is set to the string corresponding
       to the command to be executed following the trap.  Note that this
       string is reconstructed from the internal format and may not be
       formatted the same way as the original text.  The parameter is
       unset after the trap is executed.

       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.  The value of $? at the start of execution is
       the exit status of the shell or the return status of the function
       exiting.  If sig is 0 or EXIT and the trap statement is not
       executed inside the body of a function, then the command arg is
       executed when the shell terminates; the trap runs before any
       zshexit hook functions.

       ZERR, DEBUG, and EXIT traps are not executed inside other traps.
       ZERR and DEBUG traps are kept within subshells, while other traps
       are reset.

       Note that traps defined with the trap builtin are slightly
       different from those defined as `TRAPNAL () { ... }', as the
       latter have their own function environment (line numbers, local
       variables, etc.) while the former use the environment of the
       command in which they were called.  For example,

              trap 'print $LINENO' DEBUG

       will print the line number of a command executed after it has run,
       while

              TRAPDEBUG() { print $LINENO; }

       will always print the number zero.

       Alternative signal names are allowed as described under kill
       above.  Defining a trap under either name causes any trap under an
       alternative name to be removed.  However, it is recommended that
       for consistency users stick exclusively to one name or another.
