Isso funcionou para mim:
#!/bin/bash
shell=""
groups=""
user=""
home=""
exec 3>&1
dialog --separate-widget $'\n' --ok-label "Submit" \
--backtitle "Linux User Managment" \
--title "Useradd" \
--form "Create a new user" \
15 50 0 \
"Username:" 1 1 "$user" 1 10 10 0 \
"Shell:" 2 1 "$shell" 2 10 15 0 \
"Group:" 3 1 "$groups" 3 10 8 0 \
"HOME:" 4 1 "$home" 4 10 40 0 \
2>&1 1>&3 | {
read -r user
read -r shell
read -r groups
read -r home
echo $user
echo $shell
echo $groups
echo $home
#continue script here
}
exec 3>&-