pickjdk: a JDK chooser bash function

pickjdk.sh

#!/bin/bash
#
# pickjdk: provides a shell function that allows you to choose a JDK.
#
# The function sets JAVA_HOME and PATH On Linux or
# Windows, just set the environment variable JDKS_ROOT to the directory
# containing multiple versions of the JDK and the function will prompt you to
# select one. On OSX, JDKs will be discovered for you. 

# JDKS_ROOT=/opt/jdk

findjdks()
{
    JDKS=( )
    VERSIONS=( )

    # Use /usr/libexec/java_home on mac to find installed JDKs
    if [ -x /usr/libexec/java_home ]; then
        local pairs=( $(/usr/libexec/java_home -a x86_64 -V 2>&1 \
            | sort | awk -F'\t' '(NF==3){split($1,a,","); print a[1] ":" $3}') )
        for p in ${pairs[@]}; do
            JDKS[${#JDKS[@]}]=${p##*:}
            VERSIONS[${#VERSIONS[@]}]=${p%%:*}
        done
    else
        for jdk in $JDKS_ROOT/*; do
            local version=$(basename $jdk)
            if [ ! -x $jdk/bin/java ]; then
                continue
            fi
            JDKS[${#JDKS[@]}]=$jdk
            VERSIONS[${#VERSIONS[@]}]=$version
        done
    fi
    [ ${#JDKS[@]} -ne 0 ]
}

pickjdk()
{
    ## Load JDKs
    if ! findjdks; then
        echo 'error: no jdks found!' 1>&2
        return 1
    fi

    ## Add 'None' menu item
    JDKS[${#JDKS[@]}]=None
    VERSIONS[${#VERSIONS[@]}]=None

    local i= currjdk=$JAVA_HOME choice=

    ## Print menu in interactive mode (no args)
    for n in $(seq 0 $[ ${#JDKS[@]} - 1 ]); do
        i=$[ $n + 1 ]
        if [ -z "$1" ]; then
            echo -n " $i) ${VERSIONS[$n]}"
            if [ "${JDKS[$n]}" = "$currjdk" ]; then
                echo " < CURRENT"
            else
                echo
            fi
        fi
    done

    ## Determine JDK to set up
    if [ "$1" ]; then		# Process command-line choice
        if [ -z "${1/[0-9]/}" ] && [ $1 -le ${#JDKS[@]} ]; then
            # Simple integer - menu choice
            choice=$[ $1 - 1 ]
	fi

        if [ -z "$choice" ]; then
            # Match against version names.
            # Use reverse order to pick most recent JDK for matching version
            for n in $(seq $[ ${#JDKS[@]} - 1 ] 0); do
                if [ "${VERSIONS[$n]/$1/}" != ${VERSIONS[$n]} ]; then
                    choice=$n
                    break
                fi
            done
        fi

	if [ -z "$choice" ]; then
	    echo "error: could not find JDK matching '$1'" 1>&2
	    return 1
	fi
    elif [ ${#JDKS[@]} -gt 1 ]; then # Read menu choice
	choice=${#JDKS[@]}
        while [ -z "${JDKS[$choice]}" ]; do
            echo -n "Choose one of the above [1-${#JDKS[@]}]: "
            read choice
            [ -z "${choice/[0-9]/}" ] && choice=$[ $choice - 1 ]
        done
    else			# Only one JDK so we don't have a choice
        choice=0
    fi

    [ -z "$currjdk" ] && currjdk=$(dirname $(dirname $(type -path java)))

    ## Set (or unset) JAVA_HOME
    if [ ${JDKS[$choice]} != None ]; then
        export JAVA_HOME=${JDKS[$choice]}
    else
        unset JAVA_HOME
    fi

    ## Set or replace JDK in PATH
    local unset_jdk=
    for jdk in ${JDKS[*]}; do
        if [ "$currjdk" = "$jdk" ]; then
            unset_jdk=$jdk
            break
        fi
    done
    if [ "$unset_jdk" ]; then
        if [ -z "$JAVA_HOME" ]; then
            PATH=$(echo $PATH | sed "s|$unset_jdk/bin:*||g")
        else
            PATH=$(echo $PATH | sed "s|$unset_jdk|$JAVA_HOME|g")
        fi
    elif [ "$JAVA_HOME" ]; then
        PATH="$JAVA_HOME/bin:$PATH"
    fi

    ## Announce new version and clean up
    [ "${VERSIONS[$choice]}" != None ] && echo "New JDK: ${VERSIONS[$choice]}"
    hash -r
    unset JDKS VERSIONS
}