How to `cat << 'EOF'` within `su $user <<EOF`?

Question

##!/bin/bash
set -e
backup_dir='/home/my/backup'
user='my'

su $user <<EOFHD
cat << 'EOF' > $backup_dir/autorestartnftables.sh
#!/bin/bash
SERVICENAME="nftables"

# return value is 0 if running
STATUS=$?
if [[ "$STATUS" -ne "0" ]]; then
        echo "Service '$SERVICENAME' is not curently running... Starting now..."
        systemctl start $SERVICENAME
fi
EOF
chmod +x $backup_dir/autorestartnftables.sh
EOFHD

Above script is used to create autorestartnftables.sh,expect result as below:

#!/bin/bash
SERVICENAME="nftables"
# return value is 0 if running
STATUS=$？
if [[ "$STATUS" -ne "0" ]]; then
        echo "Service '$SERVICENAME' is not curently running... Starting now..."
        systemctl start $SERVICENAME
fi

autorestartnftables.sh after run sudo bash ./example.sh:

#!/bin/bash
SERVICENAME="nftables"
# return value is 0 if running
STATUS=0
if [[ "" -ne "0" ]]; then
        echo "Service '' is not curently running... Starting now..."
        systemctl start 
fi

Where is the problem?

Answer 1

Do not nest, nest, nest. Instead use declare -f and functions to transfer work to unrelated context.

##!/bin/bash
set -e
backup_dir='/home/my/backup'
user='my'
work() {
    cat << 'EOF' > $backup_dir/autorestartnftables.sh
#!/bin/bash
SERVICENAME="nftables"

# return value is 0 if running
STATUS=$?
if [[ "$STATUS" -ne "0" ]]; then
        echo "Service '$SERVICENAME' is not curently running... Starting now..."
        systemctl start $SERVICENAME
fi
EOF
    chmod +x $backup_dir/autorestartnftables.sh
}
su "$user" bash -c "$(declare -p backup_dir); $(declare -f work); work"

In this case, you could check if the user running your script is the user you want and then restart your script with that user:

##!/bin/bash
set -e
backup_dir='/home/my/backup'
user='my'
if [[ "$USER" != "$user" ]]; then
   # restart yourself as that user
   exec sudo -u "$user" "$0" "$@"
fi

cat << 'EOF' > $backup_dir/autorestartnftables.sh
#!/bin/bash
SERVICENAME="nftables"

# return value is 0 if running
STATUS=$?
if [[ "$STATUS" -ne "0" ]]; then
        echo "Service '$SERVICENAME' is not curently running... Starting now..."
        systemctl start $SERVICENAME
fi
EOF
chmod +x $backup_dir/autorestartnftables.sh

Check your scripts with shellcheck.