Find pom in subdirectories and execute mvn clean

Something like this should probably work:

find . -name "pom.xml" -exec mvn clean -f '{}' ;

in general, you would want to issue mvn clean on the parent pom, which would clean all children defined as modules, too.

If you don't have and don't want such a parent you'll need to use brute force for this, meaning something like

for dir in yourdirectory;
do
  cd $dir
  if [ -f pom.xml ];
  then
    mvn clean
  fi
done