Reusing environment variables between tasks in Ansible - bash

Question

I'm running a few tasks in a playbook which runs a bash script and registers its output:
playbook.yml:
- name: Compare FOO to BAZ
shell: . script.sh
register: output
- name: Print the generated output
debug:
msg: "The output is {{ output }}"
- include: Run if BAZ is true
when: output.stdout == "true"
script.sh:
#!/bin/bash
FOO=$(curl example.com/file.txt)
BAR=$(cat file2.txt)
if [ $FOO == $BAR ]; then
export BAZ=true
else
export BAZ=false
fi
What happens is that Ansible registers the output of FOO=$(curl example.com/file.txt) instead of export BAZ.
Is there a way to register BAZ instead of FOO?
I tried running another task that would get the exported value:
- name: Register value of BAZ
shell: echo $BAZ
register: output
But then I realized that every task opens a separate shell on the remote host and doesn't have access to the variables that were exported in previous steps.
Is there any other way to register the right output as a variable?

Answer 1

I've come up with a workaround, but there must be an other way to do this...
I added a line in script.sh and cat the file in a seperate task
script.sh:
...
echo $BAZ > ~/baz.txt
then in the playbook.yml:
- name: Check value of BAZ
shell: cat ~/baz.txt
register: output

Answer 2

This looks a bit like using a hammer to drive a screw... or a screwdriver to plant a nail. Decide if you want to use nails or screws then use the appropriate tool.
Your question misses quite a few details so I hope my answer wont be too far from your requirements. Meanwhile here is an (untested and quite generic) example using ansible to compare your files and run a task based on the result:
- name: compare files and run task (or not...)
hosts: my_group
vars:
reference_url: https://example.com/file.txt
compared_file_path: /path/on/target/to/file2.txt
# Next var will only be defined when the two tasks below have run
file_matches: "{{ reference.content == (compared.content | b64decode) }}"
tasks:
- name: Get reference once for all hosts in play
uri:
url: "{{ reference_url }}"
return_content: true
register: reference
delegate_to: localhost
run_once: true
- name: slurp file to compare from each host in play
slurp:
path: "{{ compared_file_path }}"
register: compared
- name: run a task on each target host if compared is different
debug:
msg: "compared file is different"
when: not file_matches | bool
Just in case you would be doing all this just to check if a file needs to be updated, there's no need to bother: just download the file on the target. It will only be replaced if needed. You can even launch an action at the end of the playbook if (and only if) the file was actually updated on the target server.
- name: Update file from reference if needed
hosts: my_group
vars:
reference_url: https://example.com/file.txt
target_file_path: /path/on/target/to/file2.txt
tasks:
- name: Update file on target if needed and notify handler if changed
get_url:
url: "{{ reference_url }}"
dest: "{{ target_file_path }}"
notify: do_something_if_changed
handlers:
- name: do whatever task is needed if file was updated
debug:
msg: "file was updated: doing some work"
listen: do_something_if_changed
Some references to go further on above concepts:
uri module
get_url module
slurp module
delegating tasks in ansible
registering output of tasks
run_once
handlers