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Асинхронные события (Asynchronous events)
The ed utility shall take the standard action for all signals
(see the ASYNCHRONOUS EVENTS section in Section 1.4, Utility
Description Defaults) with the following exceptions:
SIGINT The ed utility shall interrupt its current activity,
write the string "?\n" to standard output, and return
to command mode (see the EXTENDED DESCRIPTION section).
SIGHUP If the buffer is not empty and has changed since the
last write, the ed utility shall attempt to write a
copy of the buffer in a file. First, the file named
ed.hup in the current directory shall be used; if that
fails, the file named ed.hup in the directory named by
the HOME environment variable shall be used. In any
case, the ed utility shall exit without writing the
file to the currently remembered pathname and without
returning to command mode.
SIGQUIT The ed utility shall ignore this event.
