As you mention, it should be do-able with iterators rather than requiring interprocess pipes. Some idle doodling came up with a syntax that appeals to me and might appeal to you.

  # chain_lines takes a list of coderefs
  # The first sub in the chain is called with no input; subsequent one
+s are called
  # with $_ set to the line from the previous sub; the iterator return
+s one line of
  # output from the last sub in the chain. If a sub yields undef, proc
+essing
  # restarts at the first sub. When the first sub yields undef, the it
+erator is done.
  my $i = chain_lines sub { <$in> },
                      sub { /^42/ ? $_ : undef },    # grep
                      sub { join "\t", (split /\t/)[1,3,8] };
  # all_lines expands the iterator into a list of lines
  sort all_lines($i);
[download]

The grep case might warrant its own special syntax, like

grep_lines {/^42/}
[download]

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