$ perl
$SIG{'ALRM'} = sub { die "alrm received"; };
alarm 2;
my $re = ('a*' x80).'(b|c)';
my $str = "a" x 80;
$str =~ /$re/;
__END__
 ... runs forever ...

$ PERL_SIGNALS=unsafe perl
$SIG{'ALRM'} = sub { die "alrm received"; };
alarm 2;
my $re = ('a*' x80).'(b|c)';
my $str = "a" x 80;
$str =~ /$re/;
__END__
alrm received at - line 1.