Editing dynamic field name in logstash

[sahere37 (LR)]

hi, I have a log in which each line has a field with different name like below. is it possible to change all of these field's names to just "day"?
<123>day=.... ===> day=....
<678>day=.... ===> day=....

[Alex_Salgado-Elastic (Alex Salgado)]

@sahere37

hi, I have a log in which each line has a field with different name like below. is it possible to change all of these field's names to just "day"?
<123>day=.... ===> day=....
<678>day=.... ===> day=....

Try with gsub filter:

Mutate filter plugin | Logstash Reference [8.14] | Elastic