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Perl Cookbook by Nathan Torkington, Tom Christiansen

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Catching Ctrl-C

Problem

You want to intercept Ctrl-C, which would otherwise kill your whole program. You’d like to ignore it or run your own function when the signal is received.

Solution

Set a handler for SIGINT. Set it to "IGNORE" to make Ctrl-C have no effect:

$SIG{INT} = 'IGNORE';

Or, set it to a subroutine of your own devising to respond to Ctrl-C:

$SIG{INT} = \&tsktsk;

sub tsktsk {
    $SIG{INT} = \&tsktsk;           # See ``Writing A Signal Handler''
    warn "\aThe long habit of living indisposeth us for dying.\n";
}

Discussion

Ctrl-C isn’t directly affecting your program. The terminal driver processing your keystrokes recognizes the Ctrl-C combination (or whatever you’ve set your terminal to recognize as the interrupt character), and sends a SIGINT to every process in the foreground process group (foreground job) for that terminal. The foreground job normally comprises all programs started from the shell on a single command line, plus any other programs run by those programs. See Section 16.0.2 earlier in this chapter for details.

The interrupt character isn’t the only special character interpreted by your terminal driver. Type stty -a to find out your current settings:

% stty -a

                  speed 9600 baud; 38 rows; 80 columns;
               
                  lflags: icanon isig iexten echo echoe -echok echoke -echonl echoctl
               
                         -echoprt -altwerase -noflsh -tostop -flusho pendin -nokerninfo
               
                         -extproc
               
                  iflags: -istrip icrnl -inlcr -igncr ixon -ixoff ixany imaxbel -ignbrk
               
                          brkint -inpck -ignpar -parmrk
               
                  oflags: opost onlcr oxtabs
               
                  cflags: cread ...

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