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

**URL:** <https://forum.ansible.com/t/whats-correct-jinja2-operator-to-do-less-than-on-a-string/21550>\
**Category:** Ansible Project\
**Created:** [May 24, 2016, 5:29pm UTC](https://forum.ansible.com/t/whats-correct-jinja2-operator-to-do-less-than-on-a-string/21550 "2016-05-24T17:29:13Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Robert\_F](https://avatars.discourse-cdn.com/v4/letter/r/9d8465/32.png) [@Robert\_F](https://forum.ansible.com/u/Robert_F)\
**Post date:** [May 24, 2016, 5:29pm UTC](https://forum.ansible.com/t/whats-correct-jinja2-operator-to-do-less-than-on-a-string/21550/1 "2016-05-24T17:29:13Z")

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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.

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**Author:** ![Josh\_Smift1](https://avatars.discourse-cdn.com/v4/letter/j/bcef8e/32.png) [@Josh\_Smift1](https://forum.ansible.com/u/Josh_Smift1)\
**Post date:** [May 24, 2016, 5:39pm UTC](https://forum.ansible.com/t/whats-correct-jinja2-operator-to-do-less-than-on-a-string/21550/2 "2016-05-24T17:39:28Z")

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Hmm, this trivial playbook works for me:

&nbsp;&nbsp;- hosts: localhost  
&nbsp;&nbsp;&nbsp;&nbsp;tasks:  
&nbsp;&nbsp;&nbsp;&nbsp;- debug: msg="Yep!"  
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;when: server\_num \< '03'

With '--extra-vars server\_num=02', I get

&nbsp;&nbsp;TASK: [debug msg="Yep!"]

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<div class="post-metadata">

**Author:** ![Robert\_F](https://avatars.discourse-cdn.com/v4/letter/r/9d8465/32.png) [@Robert\_F](https://forum.ansible.com/u/Robert_F)\
**Post date:** [May 24, 2016, 5:56pm UTC](https://forum.ansible.com/t/whats-correct-jinja2-operator-to-do-less-than-on-a-string/21550/3 "2016-05-24T17:56:41Z")

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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.

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**Author:** ![sivel](https://sea1.discourse-cdn.com/ansible/user_avatar/forum.ansible.com/sivel/32/1198_2.png) [@sivel](https://forum.ansible.com/u/sivel)\
**Post date:** [May 24, 2016, 6:01pm UTC](https://forum.ansible.com/t/whats-correct-jinja2-operator-to-do-less-than-on-a-string/21550/4 "2016-05-24T18:01:30Z")

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The less than operator is documented at [http://jinja.pocoo.org/docs/dev/templates/#comparisons](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](http://docs.ansible.com/ansible/playbooks_filters.html#version-comparison-filters)

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<div class="post-metadata">

**Author:** ![Robert\_F](https://avatars.discourse-cdn.com/v4/letter/r/9d8465/32.png) [@Robert\_F](https://forum.ansible.com/u/Robert_F)\
**Post date:** [May 24, 2016, 6:07pm UTC](https://forum.ansible.com/t/whats-correct-jinja2-operator-to-do-less-than-on-a-string/21550/5 "2016-05-24T18:07:10Z")

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I see. I agree that doing math on strings is somewhat questionable. I’ll check out version\_compare. Thanks Matt.

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<div class="post-metadata">

**Author:** ![Josh\_Smift1](https://avatars.discourse-cdn.com/v4/letter/j/bcef8e/32.png) [@Josh\_Smift1](https://forum.ansible.com/u/Josh_Smift1)\
**Post date:** [May 24, 2016, 6:13pm UTC](https://forum.ansible.com/t/whats-correct-jinja2-operator-to-do-less-than-on-a-string/21550/6 "2016-05-24T18:13:42Z")

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

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-Josh (jbs@care.com)

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