Correct way to check Java version from BASH script

Question

How can I check whether Java is available (in the PATH or via JAVA_HOME) from a bash script and make sure the version is at least 1.5?

Answer 1

I wrote a bash function that should work for JDK 9 and JDK 10.

#!/bin/bash

# returns the JDK version.
# 8 for 1.8.0_nn, 9 for 9-ea etc, and "no_java" for undetected
jdk_version() {
  local result
  local java_cmd
  if [[ -n $(type -p java) ]]
  then
    java_cmd=java
  elif [[ (-n "$JAVA_HOME") && (-x "$JAVA_HOME/bin/java") ]]
  then
    java_cmd="$JAVA_HOME/bin/java"
  fi
  local IFS=$'\n'
  # remove \r for Cygwin
  local lines=$("$java_cmd" -Xms32M -Xmx32M -version 2>&1 | tr '\r' '\n')
  if [[ -z $java_cmd ]]
  then
    result=no_java
  else
    for line in $lines; do
      if [[ (-z $result) && ($line = *"version \""*) ]]
      then
        local ver=$(echo $line | sed -e 's/.*version "\(.*\)"\(.*\)/\1/; 1q')
        # on macOS, sed doesn't support '?'
        if [[ $ver = "1."* ]]
        then
          result=$(echo $ver | sed -e 's/1\.\([0-9]*\)\(.*\)/\1/; 1q')
        else
          result=$(echo $ver | sed -e 's/\([0-9]*\)\(.*\)/\1/; 1q')
        fi
      fi
    done
  fi
  echo "$result"
}

v="$(jdk_version)"
echo $v

This returns 8 for Java 8 ("1.8.0_151" etc), and 9 for Java 9 ("9-Debian" etc), which should make it easier to do the further comparison.

Answer 2

Using bashj, an extended bash version (https://sourceforge.net/projects/bashj/), you get a rather compact solution:

#!/usr/bin/bashj
echo System.getProperty("java.runtime.version")

The answer is provided by an integrated JVM (in ~0.017'' execution time for the script , and ~0.004'' for the call itself).

Answer 3

I know this is a very old thread but this will still be of help to others.

To know whether you're running Java 5, 6 or 7, firstly type java -version.

There will be a line in your output that looks similar to this: java version "1.7.0_55"

Then you use this table for converting the 'jargon' result to the version number.

1.7.0_55 is Java 7
1.6.0_75 is Java 6
1.5.0_65 is Java 5

Information taken from a page on the Oracle site
http://www.oracle.com/technetwork/java/javase/7u55-relnotes-2177812.html