xwd(1) on Linux
The text b5b6244c2a96, as Debian 11 (Bullseye), Debian 10 (Buster) shipped it.
dump an image of an X window
Flags it lists
-
-add -
-display -
-frame -
-help -
-icmap -
-id -
-name -
-nobdrs -
-out -
-root -
-screen -
-silent -
-version -
-xy