Find a suitable Java Virtual Machine on Mac OS X which matches a min/max version requirement

findJVMbyMinMaxJavaRequirement.sh

#!/bin/bash

function get_java_version_from_cmd() {
  # second sed command strips " and -ea from the version string
  echo $("$1" -version 2>&1 | awk '/version/{print $NF}' | sed -E 's/"//g;s/-ea//g')
}

function get_comparable_java_version() {
  # cleaning: 1) remove leading '1.'; 2) remove 'a-Z' and '-*+' (e.g. '-ea'); 3) replace '_' with '.'
  local cleaned=$(echo "$1" | sed -E 's/^1\.//g;s/[a-zA-Z+*\-]//g;s/_/./g')
  # splitting at '.' into an array
  local arr=( ${cleaned//./ } )
  # echo a string with left padded version numbers
  echo "$(printf '%02s' ${arr[0]})$(printf '%03s' ${arr[1]})$(printf '%03s' ${arr[2]})"
}

min=1.8
minC=$(get_comparable_java_version $min)
max=9
maxC=$(get_comparable_java_version $max)


# default Apple JRE plugin path
apple_jre_plugin="/Library/Java/Home/bin/java"
apple_jre_version=$(get_java_version_from_cmd "${apple_jre_plugin}")
# default Oracle JRE plugin path
oracle_jre_plugin="/Library/Internet Plug-Ins/JavaAppletPlugin.plugin/Contents/Home/bin/java"
oracle_jre_version=$(get_java_version_from_cmd "${oracle_jre_plugin}")


########################################





# find installed JavaVirtualMachines (JDK + JRE)
############################################

allJVMs=()

# read JDK's from '/usr/libexec/java_home -V' command
while read line; do
  version=$(echo $line | awk -F $',' '{print $1;}')
  path=$(echo $line | awk -F $'" ' '{print $2;}')
  path+="/bin/java"
  allJVMs+=("$version:$path")
done < <(/usr/libexec/java_home -V 2>&1 | grep '^[[:space:]]')
# unset while loop variables
unset version path

# add Apple JRE if available
if [ -x "${apple_jre_plugin}" ] ; then
  allJVMs+=("$apple_jre_version:$apple_jre_plugin")
fi

# add Oracle JRE if available
if [ -x "${oracle_jre_plugin}" ] ; then
  allJVMs+=("$oracle_jre_version:$oracle_jre_plugin")
fi



# debug output
echo ""
echo "Found:"
for i in "${allJVMs[@]}"
do
  echo $i
done



# determine JVMs matching the min/max version requirement
############################################

matchingJVMs=()

for i in "${allJVMs[@]}"
do
  # split JVM string at ':' delimiter to retain spaces in $path substring
  IFS=: arr=($i) ; unset IFS
  # [0] JVM version number
  ver=${arr[0]}
  # comparable JVM version number
  comp=$(get_comparable_java_version $ver)
  # [1] JVM path
  path="${arr[1]}"
  # construct string item for adding to the "matchingJVMs" array
  item="$comp:$ver:$path"

  # pre-requisite: current version number needs to be greater than min version number
  if [ "$comp" -ge "$minC" ] ; then

    # perform max version checks if max version requirement is present
    if [ ! -z ${max} ] ; then

      # max version requirement ends with '*' modifier
      if [[ ${max} == *\* ]] ; then

        # use the '*' modifier from the max version string as wildcard for a 'starts with' comparison
        # and check whether the current version number starts with the max version wildcard string
        if [[ ${ver} == ${max} ]]; then
          matchingJVMs+=("$item")

        # or whether the current comparable version is lower than the comparable max version
        elif [ "$comp" -le "$maxC" ] ; then
          matchingJVMs+=("$item")
        fi

      # max version requirement ends with '+' modifier -> always add this version if it's greater than $min
      # because a max requirement with + modifier doesn't make sense
      elif [[ ${max} == *+ ]] ; then
        matchingJVMs+=("$item")

      # matches 6 zeros at the end of the max version string (e.g. for 1.8, 9)
      # -> then the max version string should be treated like with a '*' modifier at the end
      #elif [[ ${maxC} =~ ^[0-9]{2}0{6}$ ]] && [ "$comp" -le $(( ${maxC#0} + 999 )) ] ; then
      #  matchingJVMs+=("$item")

      # matches 3 zeros at the end of the max version string (e.g. for 9.1, 10.3)
      # -> then the max version string should be treated like with a '*' modifier at the end
      #elif [[ ${maxC} =~ ^[0-9]{5}0{3}$ ]] && [ "$comp" -le "${maxC}" ] ; then
      #  matchingJVMs+=("$item")

      # matches standard requirements without modifier
      elif [ "$comp" -le "$maxC" ]; then
        matchingJVMs+=("$item")
      fi

    # no max version requirement -> add current version to matching list
    else
      matchingJVMs+=("$item")
    fi
  fi
done
# unset for loop variables
unset arr ver comp path item


# debug output
echo ""
echo "Matching:"
for i in "${matchingJVMs[@]}"
do
  echo $i
done



# sort the matching JavaVirtualMachines by version number
############################################

# https://stackoverflow.com/a/11789688/1128689
IFS=$'\n' matchingJVMs=($(sort -nr <<<"${matchingJVMs[*]}"))
unset IFS



# debug output
echo ""
echo "Sorted:"
for i in "${matchingJVMs[@]}"
do
  echo $i
done



# get the highest matching JVM
############################################

JAVACMD=
JAVACMD_version=

for ((i = 0; i < ${#matchingJVMs[@]}; i++));
do
  # split JVM string at ':' delimiter to retain spaces in $path substring
  IFS=: arr=(${matchingJVMs[$i]}) ; unset IFS
  # [0] comparable JVM version number
  comp=${arr[0]}
  # [1] JVM version number
  ver=${arr[1]}
  # [2] JVM path
  path="${arr[2]}"

  # use current value as JAVACMD if it's executable
  if [ -x "$path" ] ; then
    JAVACMD="$path"
    JAVACMD_version=$comp
    break
  fi
done
# unset for loop variables
unset arr comp ver path



# debug output
echo ""
echo "Highest:"
echo $JAVACMD
echo $JAVACMD_version
if [ -x "$JAVACMD" ] ; then
  echo $("${JAVACMD}" -version)
fi

Output for

min=1.7.0_79
max=1.8.0_144

on my current system:

Found:
9.0.1:/Library/Java/JavaVirtualMachines/jdk-9.0.1.jdk/Contents/Home/bin/java
9:/Library/Java/JavaVirtualMachines/jdk-9.jdk/Contents/Home/bin/java
1.8.0_144:/Library/Java/JavaVirtualMachines/jdk1.8.0_144.jdk/Contents/Home/bin/java
1.7.0_79:/Library/Java/JavaVirtualMachines/jdk1.7.0_79.jdk/Contents/Home/bin/java
9.0.1:/Library/Internet Plug-Ins/JavaAppletPlugin.plugin/Contents/Home/bin/java

Matching:
08000144:1.8.0_144:/Library/Java/JavaVirtualMachines/jdk1.8.0_144.jdk/Contents/Home/bin/java
07000079:1.7.0_79:/Library/Java/JavaVirtualMachines/jdk1.7.0_79.jdk/Contents/Home/bin/java


Sorted:
08000144:1.8.0_144:/Library/Java/JavaVirtualMachines/jdk1.8.0_144.jdk/Contents/Home/bin/java
07000079:1.7.0_79:/Library/Java/JavaVirtualMachines/jdk1.7.0_79.jdk/Contents/Home/bin/java

Highest:
/Library/Java/JavaVirtualMachines/jdk1.8.0_144.jdk/Contents/Home/bin/java
08000144
java version "1.8.0_144"
Java(TM) SE Runtime Environment (build 1.8.0_144-b01)
Java HotSpot(TM) 64-Bit Server VM (build 25.144-b01, mixed mode)

matches my JDK 7 and JDK 8.

Note that max is interpreted as lower or equal than $max!