front end - How do I extract the contents of a selected cell as plain text?

My aim is to extract the contents of an Input cells as plain text. Ideally I would like to be able to select one or more Input cells and press a button which would then extract the text from these cells as a string and assign it to a variable. However, this turns out to be harder than it seems (to me at least).

One way which was suggested in a chat conversation was to copy the cell as plain text by doing something like this

Button["Set x to selection",
  FrontEndTokenExecute[SelectedNotebook[], "CopySpecial", "PlainText"];
  x = (NotebookGet@ClipboardNotebook[])[[1, 1, 1]]

  ]

This seems to work; for example, if I type this into an input cell, select the cell, and press the button

a + b == c;
d = "x";

then x is set to the string "a+b==c;\nd=\"x\";" which is what I want. The only downside of this method as far as I can tell is that it destroys the clipboard.

To preserve the clipboard I tried using NotebookRead instead to copy the contents but I only got that to work if I changed the display form of the selected cell to "TextForm" first, e.g.

Button["Set x to selection 2",
 Module[{tmpnb, nb},

  nb = SelectedNotebook[];
  tmpnb = CreateDocument[WindowSelected -> False];
  NotebookWrite[tmpnb, NotebookRead[nb], All]; 
  FrontEndTokenExecute[tmpnb, "SelectionDisplayAs", "TextForm"];
  SelectionMove[tmpnb, All, CellContents];
  x = ToString[NotebookRead[tmpnb]];
  NotebookClose[tmpnb]]] 

Of course the downside of this approach is that it creates a temporary notebook every time I press the button.

Question

Both methods seem to do their job, but they both rely on the FrontEnd manipulating the contents of the selected cell before being able to extract the string. This made me wonder if there is an easier way to get the same result.

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Keywords:

String, Text, Cell, Export, ExportString, ToString, InputForm

Answer

Assuming nb is your notebook object, then this will do what you want without touching the clipboard:

First[FrontEndExecute[
  FrontEnd`ExportPacket[NotebookSelection[nb], "InputText"]]]

Some notes about this solution:

• It preserves evaluation semantics precisely, regardless of typesetting.


• It does not dirty the clipboard


• If you prefer to get the appearance as opposed to the evaluation semantics, you can use "PlainText" (for example, grids copy as tabular looking things as opposed to as lists)


• I tested this in 8.0.1, but it might not work in earlier versions

This FE packet only supports a limited number of formats. The public formats include "GIF", "PPM", "EnhancedMetafile" (Windows), "PICT" (Mac) , "PostScript", "RTF", "PDF", and "SVG".

I should say that the first argument of ExportPacket can also be any Notebook, Cell, or Box expression. Also, a NotebookObject, in which case it'd convert the entire notebook rather than just the selection.

When the selection does not contain a full cell it is enough to work around by using the results of NotebookRead. E.g.:

First[FrontEndExecute[ FrontEnd`ExportPacket[BoxData @ NotebookRead[nb], "PPM"]]]