Documentation actually mentions the absence of the setenv.(sh|bat)
file (by default):
(3.4) Using the "setenv" script (optional, recommended)
Apart from CATALINA_HOME and CATALINA_BASE, all environment variables
can be specified in the "setenv" script. The script is placed either
into CATALINA_BASE/bin or into CATALINA_HOME/bin directory and is
named setenv.bat (on Windows) or setenv.sh (on *nix). The file has to
be readable.
By default the setenv script file is absent. If the script file is
present both in CATALINA_BASE and in CATALINA_HOME, the one in
CATALINA_BASE is preferred.
For example, to configure the JRE_HOME and CATALINA_PID variables you
can create the following script file:
On Windows, %CATALINA_BASE%\bin\setenv.bat:
set "JRE_HOME=%ProgramFiles%\Java\jre@MIN_JAVA_VERSION@"
exit /b 0
On *nix, $CATALINA_BASE/bin/setenv.sh:
JRE_HOME=/usr/java/latest
CATALINA_PID="/run/tomcat.pid"
https://github.com/apache/tomcat/blob/10.1.9/RUNNING.txt#L151
export JRE_HOME=...
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