run sub-process of a urxvt perl extension in calling urxvt window

I am trying to write a rxvt-unicode perl extension to do what [mrxvt PrintScreen](https://code.google.com/p/mrxvt/wiki/Tips#Can_I_search_the_scroll_back_buffer) does. I.e., the extension should pipe urxvt's contents to user-defined commands. The main purpose would be viewing urxvt's contents unwrapped in less -S. Here are my first attempts. (The command is still hardcoded cat -n, and including color escape codes and joining of wrapped lines is still missing.) #! perl -w use strict; sub on_user_command { my ($self, $cmd) = @_; open PIPE, "|cat -n" or die "urxvt-pipe: error opening pipe: $^E\n"; for (my $i = $self->top_row; $i nrow; $i++) { print PIPE $self->ROW_t($i), "\n"; } close PIPE or warn "urxvt-pipe: error closing pipe: $^E\n"; () } Replacing the pipe with exec_async does not help: #! perl -w use strict; sub on_user_command { my ($self, $cmd) = @_; open FH, ">/tmp/urxvt.txt" or die "urxvt-pipe: error opening file: $^E\n"; for (my $i = $self->top_row; $i nrow; $i++) { print FH $self->ROW_t($i), "\n"; } close FH or warn "urxvt-pipe: error closing file: $^E\n"; $self->exec_async("cat", "-n", "/tmp/urxvt.txt"); () } The problem with both is that the cat runs inside urxvt's parent (e.g. another urxvt or an emacs buffer if I call urxvt as the "compile" command during extension development). I would like it to run in the instance whose contents I'm piping, or a new tab thereof. Is that possible? Obviously as a workaround, the exec_async could be modified to open a new window: $self->exec_async("urxvt", "-title", "less urxvt scrollback", "-e", "less", "-S", "/tmp/urxvt.txt"); But I'd prefer the same window, and also rather avoid creating a temporary file.