This will interpose the
.bp (break page)
request between two files to be formatted.
 If you're using only cat and a single echo, you can use this command instead:$
echo .bp | cat file1 - file2 | nroff
The cattells cat to read its standard input (in this case, from the pipe and the echo) at that point. nroff gets exactly the same input.
Parentheses are also very useful in the Bourne shell if you want to put an entire sequence of commands separated by semicolons into the background. In the C shell, the command line below will go immediately into the background.
But in the Bourne shell, the background request (
will only apply to the second command, forcing you
to wait for completion of the first job before you
get back the system prompt.
To get right back to
work, you can type:
(nroff -ms file1; nroff -ms file2) &
; nroff -ms file1 > file.out) & 22670 %
The file file.out will be created in the somewhere-else directory.
Article 13.8 shows another method for the Bourne shell. It's more limited but can also be more efficient.