The command ARG is to be read and executed when the shell receives
signal(s) SIGNAL_SPEC. If ARG is absent (and a single SIGNAL_SPEC
is supplied) or `-', each specified signal is reset to its original
value. If ARG is the null string each SIGNAL_SPEC is ignored by the
shell and by the commands it invokes. If a SIGNAL_SPEC is EXIT (0)
the command ARG is executed on exit from the shell. If a SIGNAL_SPEC
is DEBUG, ARG is executed after every simple command. If the`-p' option
is supplied then the trap commands associated with each SIGNAL_SPEC are
displayed. If no arguments are supplied or if only `-p' is given, trap
prints the list of commands associated with each signal. Each SIGNAL_SPEC
is either a signal name in <signal.h> or a signal number. Signal names
are case insensitive and the SIG prefix is optional. `trap -l' prints
a list of signal names and their corresponding numbers. Note that a
signal can be sent to the shell with "kill -signal $$".
