use Text::Balanced 'extract_tagged';
use Data::Dumper;

sub get_ifs {
	my $str=shift;
	my $list=shift || [];

	my ($extracted,
        $remainder,
        $prefix,
        $open,
        $inside,
        $close)=extract_tagged($str,"IF","ENDIF","(?s).*?(?=IF)");
	if ($extracted) {
		push @$list,$extracted;
		get_ifs($inside,$list);
		get_ifs($remainder,$list) if $remainder;
	}
	return $list;
}

print Dumper(get_ifs(<<ENDOFIFS));
IF(A) anytext
	IF(B)
		IF(C) anytext ENDIF
		IF(D) anytext ENDIF
	ENDIF
ENDIF
ENDOFIFS