FAQ 8.13 How do I trap control characters/signals?

FAQ 8.13 How do I trap control characters/signals?

am 11.03.2005 12:03:00 von brian d foy

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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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