What's correct Jinja2 operator to do "less than" on a string?

[Robert F]

I'm setting an Ansible fact like this:

    set_fact: server_num={{ ansible_hostname[-2:] }}

server_num can take these values:

    '00'

    '01'

    '02'

    '03'

    '04'

    ad infinitum

If I want a conditional that will evaluate to True for all server numbers less than a particular server number 'n' I'd like to be able to do this:

    when: server_num < 'n'

However, this throws the error "error while evaluating conditional: server_num < 'n'

I could do this but clearly it doesn't scale:

   when: server_num == '00' or server_num == '01' or ... or server_num == 'n-1'

Is there a more succinct way to do this?  I can't seem to find a Jinja2 "less than" operator.

Thanks.

[Josh Smift]

Hmm, this trivial playbook works for me:

- hosts: localhost
tasks:
- debug: msg="Yep!"
when: server_num < '03'

With '--extra-vars server_num=02', I get

TASK: [debug msg="Yep!"]
******************************************************
ok: [localhost] => {
"msg": "Yep!"
}


and with '--extra-vars server_num=17' I get

TASK: [debug msg="Yep!"]
******************************************************
skipping: [localhost]

Maybe you've got the 'when' in the wrong place or something? Or server_num
isn't getting set like you think it is?

-Josh (j...@care.com)

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[Robert F]

Yea, it's weird.  Sometimes "<" works for me and sometimes it doesn't.  I couldn't find this operator documented in the Jinja2 or Ansible docs and I don't recall where I first learned it so I figured maybe it's an invalid operator.  I put a debug statement right before the line where I'm referencing server_num and it said it was set as I expected it to be but the statement still failed.

[Matt Martz]

The less than operator is documented at http://jinja.pocoo.org/docs/dev/templates/#comparisons

Although, trying to use mathematical operations on string values isn't exactly always straight forward.

You might get better results from the `version_compare` filter such as:

when: server_num|version_compare('100', 'lt')

See http://docs.ansible.com/ansible/playbooks_filters.html#version-comparison-filters

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Matt Martz
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[Robert F]

I see.  I agree that doing math on strings is somewhat questionable.  I'll check out version_compare.  Thanks Matt.

[Josh Smift]

RF> I see. I agree that doing math on strings is somewhat questionable.

Well, strings can be sorted, and compared in that way. I wouldn't bet on
what adding 1 to a string would do, but comparisons seem legit.

http://jinja.pocoo.org/docs/dev/templates/#comparisons is where I found
the comparisons too, FWIW.

-Josh (j...@care.com)