You can use the tee
command
NAME
tee - read from standard input and write to standard output and files
e.g.
cat account_settings/account_settings.html | tee -a assets/assets.html users/users.html
or (using input redirection)
tee -a assets/assets.html users/users.html < account_settings/account_settings.html
As noted in the manual page, tee
also outputs the contents to the terminal (standard output) - if you don't want to see that, redirect stdout to null
tee -a assets/assets.html users/users.html < account_settings/account_settings.html > /dev/null
cat foo > a > b
works.