Re: PatternLayout caching system property lookup values

Hi Stig,

On Fri, 18 Nov 2022 at 11:03, Stig Døssing
<[email protected]> wrote:
> Is there a way to disable this “permanent substitution” and get log4j to do the system property lookup for every log event, even if there is a default value? If not, should there be? System properties can be changed from inside the application, so it seems strange to assume that if a system property has a value during logging init, it will keep that same value permanently.

The `${...}` placeholders are replaced at configure time. If no value
is available, they are left as is (this is IMHO a bug).

If you want to evaluate the lookup at each logging event, just escape
the dollar sign: `$${sys:testProperty}`. At configuration time one
dollar sign will be stripped, so that the lookup will be performed at
every logging event.

Piotr