Easiest is to do:
{ rest of your script } | gpg... With shells compliant to the 2024 editingedition of the POSIX specification, you can do:
set -o pipefail { rest of your script } | gpg... To make sure that failure of rest of your script or gpg is not lost in the overall exit status.
exec | cmd runs 2 commands in parallel in 2 separate processes, the first one (evaluated in a child process in all shells) doing nothing without forking (exec should really have been called nofork), and with its stdout redirected to a pipe and the second (which in some shells is not done in a child) runs cmd (in a child if its external and therefore needs to be executed) with its stdin connected to the other end of a pipe.
In some shells, you can do:
exec > >(cmd) Using the (non-POSIX) process substitution feature from ksh Which runs cmd in background with its stdin connected to a pipe, and >(cmd) expands to the name of a file (which can be /dev/fd/x or /proc/self/fd/x or a named pipe depending on the system and shell) which once open for writing (as > does) gets you the other end of the pipe.
The exit status of cmd is lost in that case.
That you can do by hand by using a temporary named pipe:
mkfifo fifo || exit cmd < fifo & cmd_pid=$! exec > fifo rest of the script ret=$? exec >&- wait "$cmd_pid" || ret=$? rm -f fifo exit "$ret" (not handling the cleanup of the fifo if the script is killed).
Bearing in mind that there's still no command in POSIX (other than m4) to give you a unique temp file reliably, let alone one of type fifo.