It outputs the major java version of the input class file, or the major java version of each class file contained in the input directory.

checkjavaversion.sh

#!/bin/bash

root=$1

VERSION=""
function major_to_version {
    local major="$1"
    case $major in
        46)  VERSION="1.2";;
        47)  VERSION="1.3";;
        48)  VERSION="1.4";;
        49)  VERSION="1.5";;
        50)  VERSION="1.6";;
        51)  VERSION="1.7";;
        52)  VERSION="1.8";;
        *)   VERSION="major $major"
    esac
}

function get_version {
    local class_file="$1"
    local major=`javap -verbose $class_file | grep "major" | cut -d ':' -f 2 | tr -d ' '`
    major_to_version $major
}

if [ -d $root ]; then
    for f in `find $root -name *.class`; do
        get_version $f
        echo "$VERSION"
    done
else
    get_version $root
    echo "$VERSION"
fi