interfacing.asciidoc: Fix some errors in the interactive sample

Fixes #1891

doc/interfacing.asciidoc

@@ -62,8 +62,8 @@ The common pattern to do that is to use a fifo buffer:
      # run command detached from the shell
      ( run command here > ${output} ) > /dev/null 2>&1 < /dev/null &
      # Open the file in Kakoune and add a hook to remove the fifo
-     echo "edit! -fifo %{output} *buffer-name*
-           hook buffer BufClose .* %{ nop %sh{ rm -r $(dirname ${output}} }"
+     echo "edit! -fifo ${output} *buffer-name*
+           hook buffer BufClose .* %{ nop %sh{ rm -r $(dirname ${output})} }"
 }
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