Bash: executing commands from within a chroot and switch user

chroot /chroot_dir /bin/bash -x <<'EOF'
su -
./startup.sh
EOF

basic option:

cat << EOF | chroot /chroot_dir 
touch aaaaa
touch bbbbb
EOF

option with different shell (eg. if using bash but in chrooted enviroment it doesn't exists)

cat << EOF | chroot /chroot_dir /bin/sh
touch aaaaa
touch bbbbb
EOF

try

chroot /chroot_dir /bin/bash -c "su - -c ./startup.sh"

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