The opening double quote in front of the word echo is not matched by a closing double quote
Writing to a file called sources.list. will not work, the file you want is sources.list (no trailing dot)
Redirecting output from an echo command with only a single > overwrites the sources.list file, getting rid of all the existing content - which means the apt command cannot be used to do any further updates of the OS after running this incorrect command. If you want to add an additional source to the list you must use two arrows, >> to append to the file - not overwrite it.
My mistake, I did not notice the scroll bar on my screen. The command line was not formatted on multiple lines and the text I could see was cut off at list. with the rest of the line not visible.
I was cutting and pasting one line at a time from the visible screen. So if one failed I could see the error message before pasting in the next one.
Would it be worth splitting up the command into shorter lines and including \s at the end of each physical line?
i’m not sure if some one who is in charge of this page is reading this forums. But i think splitting such longer lines could make sense, maybe you could open an issue at https://github.com/owncloud/client/issues to see if some one is noticing this there.