Ansible: tips and tricks

Jinja foo filters

• Strip down a string from any special chars

  jinja2 {% set a = b | regex_replace ("[^A-Za-z0-9\-]","") %}

  That will remove all special char but -. Also in the regex ([^A-Za-z0-9\-]) the last \-] could be turned into just -], - being the last char of that sequence it will be interpreted as a litteral value.

The truncate surprise feature...

• How to truncate a string in a jinja template

  jinja2 {% set hash_string = a | hash('sha1') %} {% set a = b | truncate(45, True, hash_string[-6:]) %}

In theory, if a | length exceeds 45 chars, jinja is supposed to truncate the string and replace the last 6 chars the first 6 chars from the hash_string variable. But in real life, you might you see your string truncated only when its length exceeds 45+5 chars...

Turns out, Jinja documentation around that filter says the following:

truncate(s, length=255, killwords=False, end='...', leeway=None)

We notice that leeway parameter that is supposed to fallback to None when unspecified, well... when reading carefully what comes next, we can see an explanation in the following:

The default leeway on newer Jinja versions is 5 and was 0 before but can be reconfigured globally.

So to force truncate to effectively truncate when it should, set leeway=0, e.g:

{% set a = b | truncate(45, True, hash_string[-6:], 0) %}