It depends on how the script is being killed. A kill -9 on unix can not be trapped, nor can someone pulling the plug out the wall. That aside you can set a signal handler, here is an example that traps the Ctrl-C by setting the $SIG{INT} handler to a subroutine reference. It also has an END block just for fun (any cleanup you do in normal termination could be here and it will get run after the sig handler)

$ perl -le'$SIG{INT}=sub{print "cleanup"};sleep 100;END{print "goodbye
+"}'
# here I hit Ctrl-C
cleanup
goodbye
$
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Cheers,
R.

Note that doing anything complicated (such as calling "print") from a signal handler can lead to a memory fault and core dump if you're using a perl version < 5.8.

Another way to install signal handlers is the sigtrap pragma:

use sigtrap(die INT)

END {
##do whatever it is you need to do
}
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This will trap Ctrl-C on Unix systems (dunno about Windows) and allow you to put the appropriate action into the END block.

It is the Control-C as a DOS command that I am thinking about.

Sorry, let me DOS that for you, looks like Control-C won't break out of the sleep the same way on windows.

C:\PERL\bin>perl -le"$SIG{INT}=sub{print 'cleanup';exit 0}; while(1){s
+leep 1};  END{print 'goodbye'}"
# here I hit Control-C
cleanup
goodbye
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Update

Now we are a bit more than a one liner we may as well write a proper script. As tirwhan points out it is dangerous to do much in the signal handler. Best just to set a flag that tells your loop to exit.

#!/usr/bin/perl
use strict;
use warnings;

my $killed=0;

$SIG{INT}=sub{$killed++};

while (1) {
    # this may take some time
    sleep 1;
    last if $killed;
}
if ($killed) {
    print "cleaning up after getting a sig int\n"
}else{
    print "finished infinite loop, halting problem next\n"
}
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Cheers,
R.

Pereant, qui ante nos nostra dixerunt!

    END {defined $old_name and
         defined $new_name and
         rename($old_name, $new_name) || warn "Oops: $!"}
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