/usr/local/opt/tomcat/bin/catalina

catalina.sh

#!/bin/sh

export CATALINA_HOME="$(brew --prefix tomcat)/libexec"
export CATALINA_BASE="${CATALINA_BASE:-$(brew --prefix)/var/tomcat}"

catalina_init() {
  if [ ! -e "$CATALINA_BASE/conf" ]; then
    mkdir -p "$CATALINA_BASE"
    cp -r "$CATALINA_HOME/conf" "$CATALINA_BASE/"
  fi

  if [ ! -e "$CATALINA_BASE/conf/Catalina/localhost/" ]; then
    mkdir -p "$CATALINA_BASE/conf/Catalina/localhost/"
  fi

  for app in "$CATALINA_HOME/webapps"/*/; do
    app_name=$(basename "$app")
    context_file="$CATALINA_BASE/conf/Catalina/localhost/${app_name/ROOT/tomcat}.xml"

    if [ ! -e "$context_file" ]; then
      if [ -e "$app/META-INF/context.xml" ]; then
        cp "$app/META-INF/context.xml" "$context_file"
        sed -i "s,<Context,<Context docBase=\"\${catalina.home}/webapps/${app_name}\"," "$context_file"
      else
        printf '<?xml version="1.0" encoding="UTF-8"?>\n<Context docBase="${catalina.home}/webapps/%s" />\n' \
          "${app_name}" > "$context_file"
      fi
    fi
  done
}

if [ ! -e "$CATALINA_BASE" ]; then
  catalina_init
fi

"$CATALINA_HOME/bin/catalina.sh" "$@"

This is to leverage $CATALINA_BASE to make sure previously deployed web apps are properly migrated after brew update tomcat.