The operating system has its default ways to treat signals. Special application code is executed only if a signal handler is explicitly installed. If there is no handler, some default action will be taken, which should be documented. My system has informative man pages for "signal" in sections 7 and 2.

Setting a signal to its default behavior is documented in perlvar:

    $SIG{'INT'}  = 'DEFAULT';   # restore default action
    $SIG{'QUIT'} = 'IGNORE';    # ignore SIGQUIT
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