capturefd3.sh

#!/bin/sh

# Nothing up my sleeve...
unset ANSWER

# dupe stdout (fd 1) to a new fd, which we call TERM_OUT (redirection)
# change the shell's idea of what stdout is to be TERM_OUT (exec)
exec {TERM_OUT}>&1

# set-up a command substitution
# the command is a subshell expression, with redirection applied
#   the redirection dupes stdout again, calling the new fd $OOB here
# the subshell itself invokves dialog(1)
#   we apply redirection to this to put dialog's output back on the terminal
#   and we tell dialog to send its results to the $OOB fd we opened earlier
# OOB = out-of-band
ANSWER=$( ( dialog --output-fd $OOB --inputbox 'Speak Friend and enter' 0 0  > /dev/fd/$TERM_OUT ) {OOB}>&1 )

# Ta-da!
echo ANSWER=\<$ANSWER\>