How do I execute a custom filter that returns no output without assigning to a variable?

I have a custom filter that updates a global variable in my code and does some other stuff when called. It returns no output.

I just want to call it inside a template without assigning the output to a variable.

Doing this works but I want to remove the unnecessary variable assignment:

{%- set unused = {'one': 'aaa', "two": "bbb", 'three': 'ccc'} | get_env_var -%}

I've tried the following:

{%- {'one': 'aaa', "two": "bbb", 'three': 'ccc'} | get_env_var -%}
jinja2.exceptions.TemplateSyntaxError: tag name expected

{{'one': 'aaa', "two": "bbb", 'three': 'ccc'} | get_env_var}
jinja2.exceptions.TemplateSyntaxError: expected token 'end of print statement', got ':'

{{{'one': 'aaa', "two": "bbb", 'three': 'ccc'} | get_env_var}}
yaml.composer.ComposerError: expected a single document in the stream
in "<unicode string>", line 3, column 1:
    ccc
    ^
but found another document
  in "<unicode string>", line 4, column 1:
    ---
    ^

How do I just execute a custom filter and not capture its output?

Given that your environment already have the expression statement extension enabled, then the expression statement — {% do ... %} — is the best fit for your use case.

As pointed in the documentation, it acts like a variable expression — {{ ... }} — but won't print anything.

The usage in your case would be something like:

{%- do {
    'one': 'aaa', 
    'two': 'bbb', 
    'three': 'ccc'
} | get_env_var -%}