Manages different versions of Java in BASH.

README.md

Java Version Manager for BASH

A simple script for managing different versions of Java.

Installation

1. Create the directory .jvm in your home directory.
2. Copy jvm to .jvm.
3. Add . ~/.jvm/jvm to your .bashrc script.
4. Exit and open a new terminal window.

How It Works

• You are expected to download the desired JDK or JRE from Oracle.
• You can put the JDK or JRE wherever you want.
• You are simply adding paths that will be managed by jvm.
• You can set a default, which will be automatically made available.
• You can change the active version of Java, unique to each terminal session.

To learn how to add and remove these directories, run jvm anywhere in your shell.

jvm

#!/usr/bin/env bash

# global settings
JVM_HOME="$HOME/.jvm"
JVM_VERSIONS="$JVM_HOME/versions"
JVM_DEFAULT="$JVM_VERSIONS/default"

###
# Manages relaying commands to other JVM functions.
#
# @param string COMMAND The command to execute.
#
# @return integer Returns the status of the last command.
##
function jvm()
{
    # make sure home exists
    if [ ! -d "$JVM_HOME" ]; then
        if ! mkdir "$JVM_HOME"; then
            return 1
        fi
    fi

    # make sure versions exists
    if [ ! -d "$JVM_VERSIONS" ]; then
        if ! mkdir "$JVM_VERSIONS"; then
            return 1
        fi
    fi

    # get command name
    local COMMAND="$1"; shift

    # execute command
    case "$COMMAND" in
        add)
            jvm_add "$@"
            ;;
        default)
            jvm_default "$@"
            ;;
        list)
            jvm_list
            ;;
        remove)
            jvm_remove "$@"
            ;;
        use)
            jvm_use "$@"
            ;;
        *)
            jvm_usage
            ;;
    esac

    return $?
}

###
# Adds a version to manage.
#
# @param string VERSION   The JDK or JRE version.
# @param string JAVA_HOME The path to the JDK or JRE.
#
# @return integer The exit status.
##
function jvm_add()
{
    local VERSION="$1"
    local JAVA_HOME="$2"

    # check usage
    if [ '' = "$VERSION" ] || [ '' = "$JAVA_HOME" ]; then
        cat <<USAGE >&2
Usage: jvm add VERSION JAVA_HOME
Adds a JDK or JRE to manage.

VERSION
  The version of the JDK or JRE.

JAVA_HOME
  The path to the JDK or JRE.

USAGE

        return 0
    fi

    # check for reserved version
    if [ 'default' = "$VERSION" ]; then
        echo 'The version "default" is reserved.' >&2

        return 1
    fi

    # check JAVA_HOME
    if [ ! -d "$JAVA_HOME" ]; then
        echo "$JAVA_HOME: No such directory" >&2

        return 1
    fi

    if [ ! -f "$JAVA_HOME/bin/java" ]; then
        echo "$JAVA_HOME: Does not appear to be JAVA_HOME" >&2

        return 1
    fi

    # check existing link
    local NEW="$JVM_VERSIONS/$VERSION"

    if [ -e "$NEW" ]; then
        if ! rm "$NEW"; then
            return 1
        fi
    fi

    # create link
    if ! ln -s "$JAVA_HOME" "$NEW"; then
        return 1
    fi
}

###
# Cleans up an initialized environment.
##
function jvm_clean()
{
    if [ -e "$JVM_ACTIVE" ]; then
        rm "$JVM_ACTIVE"
    fi
}

###
# Sets or displays the deafult JDK or JRE.
#
# @param string VERSION The JDK or JRE version to make default.
#
# @return integer The exit status.
##
function jvm_default()
{
    local VERSION="$1"
    
    # display version
    if [ '' = "$VERSION" ]; then

        # check first
        if [ -e "$JVM_DEFAULT" ]; then
            basename $(readlink "$JVM_DEFAULT")
        fi

    # set version
    else

        # check for reserved version
        if [ 'default' = "$VERSION" ]; then
            echo 'The version "default" is reserved.' >&2

            return 1
        fi

        # check for existing version
        local JVM_VERSION="$JVM_VERSIONS/$VERSION"

        if [ ! -e "$JVM_VERSION" ]; then
            echo "$VERSION: Version not managed" >&2

            return 1
        fi

        # remove existing link
        if [ -e "$JVM_DEFAULT" ]; then
            if ! rm "$JVM_DEFAULT"; then
                return 1
            fi
        fi

        # set new link
        if ! ln -s "$JVM_VERSION" "$JVM_DEFAULT"; then
            return 1
        fi

    fi
}

###
# Initializes the current environment.
##
function jvm_init()
{
    local FILE=$(tempfile)

    if rm "$FILE"; then
        echo "$FILE"
    fi
}

###
# Lists the manages JDK and JREs.
##
function jvm_list()
{
    ls -1 "$JVM_VERSIONS" | grep -Pv '^default$'
}

###
# Removes a version from management.
#
# @param string VERSION The version
##
function jvm_remove()
{
    local VERSION="$1"

    # check usage
    if [ '' = "$VERSION" ]; then
        cat <<USAGE >&2
Usage: jvm remove VERSION
Removes a managed JDK or JRE.

VERSION
  The version to remove from management.

USAGE

        return 0
    fi

    # check for reserved version
    if [ 'default' = "$VERSION" ]; then
        echo 'The version "default" is reserved.' >&2

        return 1
    fi

    # remove version
    local OLD="$JVM_VERSIONS/$VERSION"

    if [ -e "$OLD" ]; then
        if ! rm "$OLD"; then
            return 1
        fi
    fi
}

###
# Displays main usage message.
##
function jvm_usage()
{
    cat <<USAGE >&2
Usage: jvm COMMAND
Manages different versions of JDKs and JREs.

COMMAND
  The command to execute:

    add      Adds a JDK or JRE to manage.
    default  Sets or displays the deafult JDK or JRE.
    list     Lists the managed JDKs and JREs.
    remove   Removes a managed JDK or JRE.
    use      Uses a managed JDK or JRE.

USAGE
}

###
# Enables the use of a JDK or JRE.
##
function jvm_use()
{
    local VERSION="$1"

    # check usage
    if [ '' = "$VERSION" ]; then
        cat <<USAGE >&2
Usage: jvm remove VERSION
Removes a managed JDK or JRE.

VERSION
  The version to remove from management.

USAGE

        return 0
    fi

    # check for reserved version
    if [ 'default' = "$VERSION" ]; then
        echo 'The version "default" is reserved.' >&2

        return 1
    fi

    # check version
    local JVM_VERSION="$JVM_VERSIONS/$VERSION"

    if [ ! -e "$JVM_VERSION" ]; then
        echo "$VERSION: Version not managed" >&2

        return 1
    fi

    # check existing link
    if [ -e "$JVM_ACTIVE" ]; then
        if ! rm "$JVM_ACTIVE"; then
            return 1
        fi
    fi

    # create new link
    if ! ln -s "$JVM_VERSION" "$JVM_ACTIVE"; then
        return 1
    fi

    # set java home
    export JAVA_HOME="$JVM_VERSION"
}


# create directory placeholder
if JVM_ACTIVE=$(jvm_init); then

    # clean up on exit
    trap jvm_clean EXIT

    # add to path
    export PATH="$JVM_ACTIVE/bin:$PATH"

    # activate default
    if [ -e "$JVM_DEFAULT" ]; then
        jvm_use "$(basename "$(readlink "$JVM_DEFAULT")")"
    fi

fi