check-jvm-env-vars.sh

#!/usr/bin/env bash
# check-jvm-env-precedence.sh
# Pairwise precedence test for: _JAVA_OPTIONS, JAVA_TOOL_OPTIONS, JDK_JAVA_OPTIONS

set -euo pipefail

say() { printf "%s\n" "$*"; }
hr() { printf "%s\n" "----------------------------------------"; }

# Tiny source-file program
cat > Test.java <<'EOF'
public class Test {
  public static void main(String[] args) {
    System.out.println("foo=" + System.getProperty("foo"));
  }
}
EOF

# Run java with exactly two env vars set, the third removed,
# and also remove any inherited values from the parent shell.
test_pair() {
  local A="$1" B="$2"
  local aval="from-${A}" bval="from-${B}"
  local out val

  out="$(
    env -u _JAVA_OPTIONS -u JAVA_TOOL_OPTIONS -u JDK_JAVA_OPTIONS \
        "${A}=-Dfoo=${aval}" \
        "${B}=-Dfoo=${bval}" \
        java Test.java 2>&1 || true
  )"

  val="$(printf "%s\n" "$out" | awk -F'=' '/^foo=/{print $2; exit}')"
  if [[ "$val" == "$aval" ]]; then
    echo "$A"
  elif [[ "$val" == "$bval" ]]; then
    echo "$B"
  else
    say "WARN: ${A} vs ${B} produced unexpected output:"
    say "$out"
    echo "unknown"
  fi
}

rank_three() {
  local -A wins=([_JAVA_OPTIONS]=0 [JAVA_TOOL_OPTIONS]=0 [JDK_JAVA_OPTIONS]=0)
  for w in "$@"; do
    [[ "$w" == "unknown" ]] && continue
    (( wins["$w"]++ )) || true
  done
  {
    printf "_JAVA_OPTIONS %d\n" "${wins[_JAVA_OPTIONS]}"
    printf "JDK_JAVA_OPTIONS %d\n" "${wins[JDK_JAVA_OPTIONS]}"
    printf "JAVA_TOOL_OPTIONS %d\n" "${wins[JAVA_TOOL_OPTIONS]}"
  } | sort -k2,2nr | awk '{print $1}'
}

hr
say "Pairwise tests with a clean env each time:"

w1="$(test_pair _JAVA_OPTIONS JAVA_TOOL_OPTIONS)"
say "_JAVA_OPTIONS vs JAVA_TOOL_OPTIONS -> winner: $w1"

w2="$(test_pair _JAVA_OPTIONS JDK_JAVA_OPTIONS)"
say "_JAVA_OPTIONS vs JDK_JAVA_OPTIONS -> winner: $w2"

w3="$(test_pair JAVA_TOOL_OPTIONS JDK_JAVA_OPTIONS)"
say "JAVA_TOOL_OPTIONS vs JDK_JAVA_OPTIONS -> winner: $w3"

order=($(rank_three "$w1" "$w2" "$w3"))

hr
say "Final precedence, highest first:"
printf "1) %s\n" "${order[0]:-inconclusive}"
printf "2) %s\n" "${order[1]:-inconclusive}"
printf "3) %s\n" "${order[2]:-inconclusive}"

hr
say "Sanity check with all three set at once:"
env -u _JAVA_OPTIONS -u JAVA_TOOL_OPTIONS -u JDK_JAVA_OPTIONS \
  _JAVA_OPTIONS='-Dfoo=from-_JAVA_OPTIONS' \
  JAVA_TOOL_OPTIONS='-Dfoo=from-JAVA_TOOL_OPTIONS' \
  JDK_JAVA_OPTIONS='-Dfoo=from-JDK_JAVA_OPTIONS' \
  java Test.java