🚀 go-pugleaf

that did the trick! I knew it was an easy fix, I just couldn't remember where I'd read about the solution. here's the script, for those who came to beg, borrow, or steal.

(*

written, tested, and completely un-guaranteed
by David Holman (david*at*plain-clothes*dot*com)

* )

tell application "InDesign CS"
	--activate
	set the clipboard to nothing
	set origDelim to AppleScript's text item delimiters
	set myDoc to active document

	tell myDoc
		--warn if no selection or incorrect selection exists
		if selection exists then
			if class of selection is in {graphic, polygon, rectangle, image} then

				--get the file name of the linked image
				if class of selection is in {polygon, rectangle} then
					set fileName to (name of item link of all graphics of item 1 of selection) as string
				else
					set fileName to (name of item link of item 1 of selection) as string
				end if

				--extract the trans number from the file name
				try
					set AppleScript's text item delimiters to {"."}
					set noExt to first text item of fileName
					set AppleScript's text item delimiters to {"_"}
					set transNum to first text item of noExt

					--copy trans number to clipboard
					set the clipboard to transNum

				on error
					set AppleScript's text item delimiters to origDelim
					display dialog "the script failed to extract the desired portion of the file name." buttons {"damn."} default button 1
				end try

				set AppleScript's text item delimiters to origDelim
				beep

			else
				display dialog "Please select an image and retry." buttons {"oops!"} default button 1
			end if
		else
			display dialog "Please select an image and retry." buttons {"oops!"} default button 1
		end if
	end tell
end tell