You didn't really say anything about the context in which you need to do this export, but I'm assuming that you want to do this in a program, as opposed to just using the menu command File/Export from a view.
The 1-2-3 Export functionality in Notes is not directly available from LotusScript, but in macro language you can use @Command([FileExport]; "1-2-3"; filename) to export information from the current view. The user will be prompted whether to export all documents or only selected documents and whether to include view titles.
If this is not good enough, you can use LotusScript to create an export file. There are two ways to do this (assuming you do not want to have to learn the 1-2-3 file format and write your own code to produce the binary file).
First, if your code is running on a platform that supports OLE automation and has 1-2-3 installed, you can use OLE automation to create a new spreadsheet, set values and formatting for its cells, and save the resulting 123 file. There are numerous examples in the LDD Notes/Domino 4 and 5 forum and the SmartSuite forum that do exactly that.
Alternately, if OLE automation is not an option, you can create a CSV file. This is just text, with any text values enclosed in double quotes (if there are double quotes in the text, change these to double-double quotes (e.g., the string Robert "Big Bob" Malloy becomes "Robert ""Big Bob"" Malloy" in the CSV file). Number and date values are not enclosed in quotes. 1-2-3 can perfectly well understand this file type, though it doesn't allow you to format the cells.
This was first published in March 2003