ansible pass shell command result to variable

You could use the copy module in addition with local_action to save the variable to a local file on your control machine and use it later on your next playbook:

- local_action: copy content="slave_server_id: {{ slave_repli.stdout_lines[0] }}" dest=/path/to/var/file

Instead of generating your ID from within your playbook, this is where you may want to define a custom fact. On your mysql server, you'ld do something like this:

mkdir -p /etc/ansible/facts.d
cat <<EOF >/etc/ansible/facts.d/mysql.fact
#!/bin/sh
echo "[mysql]"
echo server_id=`hostname -I | sed -e 's/ \+\([a-z0-9]\+\:\)\+[a-z0-9]\+//' | sed -e 's/ /\n/' | grep -v '^$' | tail -1 | awk -F. '{print $3 * 256 + $4}'`
EOF
chmod +x /etc/ansible/facts.d/mysql.fact

Run ansible -m setup your.mysql.ip.address to make sure your fact is properly executed. You should have some ansible_local['mysql']['mysql']['server_id'] defined.

Say you'ld want ansible to deploy this fact, you may do something like:

- name: install fact
  copy: src=myfact dest=/etc/ansible/facts.d/mysql.fact owner=root group=root mode=0755
  register: fact_installed
- name: reload facts
  setup: filter=ansible_local
  when: fact_installed is defined and fact_installed.changed == True

After which, you may include your template, referring to your server_id variable.

You have two options to use the generated value in your template:

Option 1: Use slave_repli.stdout_lines in your template:

# in templates/root.j2:
...
slave_server_id: {{ slave_repli.stdout_lines[0] }}
...

Option 2: Assign a variable

In your playbook:

- name: rewrite
  vars:
    slave_server_id: "{{ slave_repli.stdout_lines[0] }}"
  template:
    src: templates/root.j2
    dest: /root/test.conf

In your template:

# in templates/root.j2:
...
slave_server_id: {{ slave_server_id }}
...

I prefer the second approach as it's much cleaner.