FAQ 8.13 How do I trap control characters/signals?


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8.13: How do I trap control characters/signals?

You don't actually "trap" a control character. Instead, that character
generates a signal which is sent to your terminal's currently
foregrounded process group, which you then trap in your process. Signals
are documented in "Signals" in perlipc and the section on "Signals" in
the Camel.

You can set the values of the %SIG hash to be the functions you want to
handle the signal. After perl catches the signal, it looks in %SIG for a
key with the same name as the signal, then calls the subroutine value
for that key.

# as an anonymous subroutine

$SIG{INT} = sub { syswrite(STDERR, "ouch\n", 5 ) };

# or a reference to a function

$SIG{INT} = \&ouch;

# or the name of the function as a string

$SIG{INT} = "ouch";

Perl versions before 5.8 had in its C source code signal handlers which
would catch the signal and possibly run a Perl function that you had set
in %SIG. This violated the rules of signal handling at that level
causing perl to dump core. Since version 5.8.0, perl looks at %SIG after
the signal has been caught, rather than while it is being caught.
Previous versions of this answer were incorrect.


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