I don't use Linux and therefore also not UEX. It looks like UEX does not have the filter feature as UltraEdit for Windows has. There can be used only the List lines containing string option to get the lines of interest output into a view window. It is possible in UltraEdit for Windows copying the lines in the Find String List view window via the context menu item Copy to clipboard of the view window to the clipboard and paste them into a new file. A Find in Files searching just in the currently opened file can be also used in UltraEdit for Windows to get lines of interest written into a new file.

I recommend comparing the full features list of UltraEdit for Windows with the full features list of UltraEdit for Mac. UltraEdit for Linux is more similar to UltraEdit for Mac than to UltraEdit for Windows. There is no such list for UltraEdit for Linux anymore since the web site relaunch. You can ask the technical support of UltraEdit, Inc. by email if you want to know for sure if UEX supports filtering a file depending on a find like UltraEdit for Windows if you don't want to wait until a UEX user replies here.