my %parents_of; my $parentid; while ( my $line = ) { if ($line =~ /^Folder (\d{3,5})\s+\-\s+.*\./) { $parentid = $1; } elsif ($line =~ /\s+subfolder\s+(\S+)\s+\-\s+.*\./) { push @{ $parents_of{ $1 } }, $parentid; } } sub build_path { my $folderid = shift @_; my @parents = @{ $parents_of{ $folderid } || [] }; return @parents ? [ map { map { "$_/$folderid" } @{ build_path( $_ ) } } @parents ] : [ $folderid ]; } foreach my $k (sort (keys (%folders))) { $folderpaths{$k} = build_path($k); print "$k => $_\n" for @{ $folderpaths{$k} }; }