LISP to update block in drawing using "-insert blkname=" approach
[You don't need to provide a filepath if the drawing file is in a place where AutoCAD knows to look.]
The potential problem I see is that INSNAME is a System Variable, holding the Block name to be offered as default for the next Insert command. It is not the name of a selected Block. If the idea is to Insert one and then immediately [never if anything else has been drawn since Insertion of the desired Block] run this command to update it [suggested by Select using Last for selection], then that should give you the right name, but will you always and only use it immediately after an Insert?
Even if the answer is Yes, you will be asked the question of whether you want to replace the definition, which your code does not address. After you've answered that, the definition change will have been accomplished, and you can cancel the Insert without finishing it -- giving it nil when it's asking for an insertion point will do. I would do this with the command part:
(command "_.insert" blknm "_yes" nil)
and having not completed the Insert, there will be no need to Erase it.
If you want to take the Block name to update from an already-Inserted Block without needing that to have happened immediately before, that's different [but not difficult, though slightly more complex if it's a dynamic Block].
@Edgetrimmer wrote:
... to pick an obsolete version of a block on screen to update from my master blocks file. ....
Is your "master blocks file" a drawing file with proper/current Block definitions in it? If so, you can't use this approach. It requires the replacing definition to be a drawing file of its own with that name, not a Block within a drawing file. Your "master blocks file" would need to be a folder containing separate drawing files, and it would need to be listed in the Support File Search Path list in OPTIONS for AutoCAD to be able to find the drawing.
