while ( my $line = <DATA> ) {
	chomp $line;

	# remove the spaces from start of line
	if ( $line =~ s/^\s+// ) {
		# print line if successful replacement
		print $line;
	}
	else {
		# print newline (not for first line)
		print "\n" if $. != 1;
		print $line;
	}
}

__DATA__
first
	second
	third
first
	second
	third
first
	second
first

##</code><code>##

while ( my $line = <DATA> ) {
	chomp $line;

	# remove the spaces from start of line
	if ( ! ( $line =~ s/^\s+// ) ) {
		# print newline (not for first line)
		print "\n" if $. != 1;
	}

	print $line;
}