The Windows version also takes JDK_HOME into consideration, maybe it would be better to have the same behaviour.

Won't this overwrite the visualvm_jdkhome if the config file is present, even if visualvm_jdkhome is not defined in it ?

We only want to override JAVA_HOME if visualvm.conf is found AND visualvm_jdkhome is defined in it.

I appreciate any insights or corrections you might have.

Won't this overwrite the visualvm_jdkhome if the config file is present, even if visualvm_jdkhome is not defined in it ?

Setting default value for luncher visualvm_jdkhome based on JDK_HOME or JAVA_HOME env.
after we check for visualvm_jdkhome in visualvm.conf (it might not be defined here ) and overide with privious JDK_HOME or JAVA_HOME env any.

We only want to override JAVA_HOME if visualvm.conf is found AND visualvm_jdkhome is defined in it.
My understanding bellow order

1. we default to env var
2. then visualvm.conf configuration (if defined , else env )
3. --jdkhome argument override env & conf

Env set with conf

Has env set & conf but ovrride with args

Only env set , no conf disabled

Your second example covers the case when the config file is in etc/
But line 66/73 overwrites the variable you set in the patch if the config file is found in lib/

if [ -f "$progdir"/../lib/visualvm/etc/visualvm.conf ] ; then visualvm_jdkhome="$basedir"

nit: set_jdk_java_home would be a better name, as this falls back to environment variables.