Project bashj : a bash mutant with java support

What ?                   

The bashj project is hosted on sourceForge. bashj is an extended bash allowing to use java libraries, methods and source code from bash scripts.

The bashj code combines

• java performance andreadability
• bash power andversatility

-> Current version 1.0 (july 2018)...

This page is an introduction to bashj, with general notes and installation guide.

There is also a bashj programming guide page.

To bash developers, bashj brings

• Readability in the java section (OO style coding)
• JVM efficiency for CPU intensive components
• modular extensibility using java packages
• floating point (double) values variable and evaluation functions
• Math tools
• Swing UI tools
• Inter process tools between multiple bash process (and java process)
• Host registry
• ...

Why ?

Java and bash are often partners in software projects.

Personnally I used both of them widely. Being rather lazy, I tried to minimize the number of necessary techonologies in my projects. These two covered 99% of my needs together. Java is perfect to translate concepts into software. But bash is necessary for various OS level tasks, like process control, deployment ... In fact I was frequently disappointed by the incapacity to reuse java results and expertise within scripts (this was only possible with heavy java process launching, and main() entry points). I was also frustrated by the strange and numerous coding conventions necessary to perform simple bash tasks. So I decided to set up and use this bashj tool.

Since bashj appeared to offer significant benefits, I decided to make it publicly available.

In terms of genetics, consider bashj as a bash mutant, whose genome has been loaded with wide portions of the java genome. 

Their possible interactions are numerous but limited in terms of integration.

With this project, any script is given the capacity to quickly and directly call java methods without creating new OS processes.

How ?

A bashj server (a java background process)  communicates with bash scripts (considered as clients).

Dedicated functions are internally defined, and used from bash script clients to request server actions.

The communication uses mainly TCP connections.

This may be also be seen as a kind of bash preprocessor : bash itself is finally called by the bashj process.

Requirements and limitations

• bash (version 4.*+)
• Linux  (kernel version 3.*+)
• java JDK (version 9+) (JRE is not enough)
• 64 bits (because Oracle dropped 32-bits support for java from version 9)
• only public static java methods (and public static fields) may be called 
• only methods with primitive types (including String) as parameters and return value (neither array, nor collections). Varargs are supported by bashj.
• no embedded invocations of java methods 
• These greek characters φ χ ψ τ have specific usage within bashj and may not be used in bashj sources

bashj is developped and tested on Linux (Ubuntu 18.04). 

It should run (without having been tested) at least on 64-bits debian-based linux systems  with the components listed above (linux kernel, bash & java).

Installation

The target installation directory is /opt/bashj . Follow carefully these steps (commands in a terminal window)

download from sourceforge bashjInstall-<version>.tar and bashj.install

go to the directory containing the downloaded files, and :

sudo chmod +x ./bashj.install

sudo ./bashj.install             # launching the installation script

For the uninstallation:

cd ; sudo /opt/bashj/bashj.install -uninstall 

Check, try and test

Various bashj scripts examples are in /var/lib/bashj/example/.Open a bash terminal window and type the following commands to discover bashj's elementary actions.

bashj -help

bashj "Math.cos(1.0)"               # check that the bashj interpreter operates

cd /var/lib/bashj/example/          # going to the example directory

ls                                  # view list of examples

cat javaLang                        # having a look at the code

./javaLang                          # running the code

cat check

./check

bashj +PP factorial                 # understanding how bashj works internally

./all                               # run all examples - shows execution speed

The same may be realized for all example scripts.

It is suggested to try, copy, adapt these examples scripts.

Configuration

No configuration is necessary.

However it is possible for the user to put various jar files under the jarlib/ directory.

All public static methods and all public static fields defined in these classes will be available in the bashj interpreter.

They should be called as indicated in the programming guide..

Annexes

Support

Please contact fil@gonze.org for support, remarks, suggestions,...

bashj interactive commands

The bashj script may be called as interpreter, or interactively for various actions. Use  bashj -help  to see this:

[bashj] - administrative taks - no server required
 bashj -help    : show this
 bashj -status  : server status
 bashj -stop    : stops the server
 bashj -restart : (re-)starts the server

 bashj -trace   : show server trace
 bashj -out     : check server stdOut (normally empty)
 bashj -err     : check server stdErr (normally empty)
 bashj -Trace   : follow server trace

 . bashj =      : enable interactive java calls from bash session
   (type again 'bashj -help' for more help when session is enabled)

[bashj] - interacting with server (launched if necessary)
 bashj +classes <filter>  : lists classes accessible to bashj clients
 bashj +methods <filter>  : lists methods accessible to bashj clients
 bashj +fields  <filter>  : lists fields  accessible to bashj clients
 bashj +status            : server status
 bashj +info              : server line status
 bashj +pp <bashj file>   : preprocessor output
 bashj +PP <bashj file>   : preprocessor analysis
 bashj +ex <example>      : run and check example bashj script
 bashj +eval <expression> : call the double eval method
 bashj +uDoc              : list utility methods from class u (bashj.u)

 bashj + <call() expression(s)> : verbosely evaluate java call(argument)
            example:  bashj + "Math.hypot(3.0,4.0)" "Math.PI" "u.classes()" 
 bashj <call() expression(s)> : evaluate java call(argument)
            example:  bashj "Math.hypot(3.0,4.0)" "Math.PI" "u.classes()"

bashj interpreter mode

During a normal interactive bash session, it is possible to enable java calls provided by bashj. To enable the java calls , type this command:

. bashj =

And from there, the user is allowed to mix bash commands with j-prefixed commands including java calls.

[bashj] bash interpreter with interactive java calls enabled
 enter simple bash commands, like 'ls -l' , 'ps' ...
 enter j-prefixed bash(j) commands, like :
       j echo "cos[3]=Math.cos(3)"
       j HYPOT="Math.hypot(3,4)"

In interpreter mode, thejoperates as a prefix. The command following this prefix (it is actually a bash function) is processed as if it was included in a bashj script.

Installed files

The files are installed under /opt/bashj/, and include:

• bashjInstall<version>.tar (a tar file containing all bashj required files)
• bashj (the central script, including the command interpreter - a link is created in /usr/bin)
• bashj.install (installation script)
• bashj.wrk (auxiliary script)
• bashjServer.jar (a jar containing the compiled java class bashj.server.class)
• README (a readme file - short intro to this wiki page)
• example/ (a subdirectory with various example scripts (executable files))
• jarlib/ (a subdirectory with the jars choosen by the user to make the involved classes available  to bashj)
• maps/ (a subdirectory with the persistent maps) 

Working transient files are dynamically created in /dev/shm/bashj, with the following subdirectories

• classes/ The dynamically created java classes
• srv/ server related data (pid, stdout, stderr)

Speed notes

The execution time of bashj  is excellent due to several factors:

• TCP efficiency
• in-memory dynamic java compiling
• cache-based java class loading
• JVM global efficiciency

Simple tests (on a 2018 average machine) indicate that a basic java method call requires around 1 msec. This probably depends on TCP config parameters.

The startup time for a bashj script hosting java methods is around 8 msec.

For a java call involving heavy CPU load, the execution delay for the call is the same as in a direct JVM.

For the minimal "Hello world" program, the minimal and median execution times are roughly:

	minimum (msec)	median (msec)
bash	2	6
bashj	7	11
java	72	80

And this shows that in some cases, executing a simple java program from its main() entrypoint is faster with bashj than with java itself ! 

Future Improvements

• ? Create an installable package for debian distribs
• ? Organize the bashj server as a Linux service