Not a concern with pbcopy, but worth mentioning in general: whatever the process substitution outputs is also seen by the next pipe segment, after the original input; e.g.: seq 3 | tee >(cat -n) | cat -e (cat -n numbers the input lines, cat -e marks newlines with $; you'll see that cat -e is applied to both the original input (first) and (then) the output from cat -n). Output from multiple process substitutions will arrive in non-deterministic order. – mklement0 Dec 9 '14 at 4:47
Why would you try that. Tee is designed to send what you see on the screen to a file at the same time, not designed for the way you want to use it.
From the man page for tee:
tee - read from standard input and write to standard output and files
What would be wrong with just doing the send twice, once to each destination. If you know the source filesystem is static then there would be no differences in the results.
-f <outfile>
output is normally written to standard output so it can be,
for example, piped to btrfs receive. Use this option to write
it to a file instead.