I want to guard against double-counting, as with 01j01.txt or 01j02.txt vs
02j01.txt, and that requires some heavy-duty concentration.
"My" solution (since my first post in this thread) joins one file with all
the other files. Not pairwise. There is nothing to concatenate at the end.
I have a script that does a nice job of grouping the duplicated hostnames,
but it won't separate them with blank lines ... (yet).
"My" solution (since my first post in this thread) outputs the hostnames in
order. They are already grouped. To prepend them with blank lines, the
output of every join can be piped to:
awk '$1 != p { p = $1; print "" } { print }'
