sub put_brackets
{
	my( $str, @pats ) = @_;
	my $mask = ' ' x length $str;
	my $ofs = 0;
	for ( @pats )
	{
		$ofs = index $str, $_, $ofs;
		last if $ofs < 0; # this pattern not found; look for no more.
		substr $mask, $ofs, length($_), 'a' x length($_);
	}
	# print "string= '$str'\n";
	# print "mask  = '$mask'\n";

	join '', map sprintf(
		/a/ ? '[%s]' : '%s',
		substr $str, 0, length($_), ''
	), split /\b/, $mask
}