Scala as a shell script: jars on the classpath

Question

You can run a scala script as a linux shell script:

#!/bin/sh
exec scala "$0" "$@"
!#

println("Hello")

In one such script I need to load classes from a group of jars (which happen to be in the same directory as the script). If this were the REPL I could use :jar, but that's not available in script mode.

I'm trying to set the -classpath parameter:

#!/bin/sh
exec scala -classpath '.:./*.jar' "$0" "$@"
!#

import javax.media.jai.{JAI, RenderedOp}

but the compiler just can't find the classes:

error: object media is not a member of package javax
import javax.media.jai.{JAI, RenderedOp}
             ^

How do I include these jars?

Using ' will prevent glob expansion, so it will look for a file named *.jar. — Daniel C. Sobral
– Daniel C. Sobral, Commented Nov 25, 2011 at 2:04

viktortnk · Accepted Answer · 2011-11-24 10:12:43Z

10

exec scala -classpath ./*.jar $0 $@

will work

answered Nov 24, 2011 at 10:12

viktortnk

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2 Comments

Marcus Downing Over a year ago

No, it doesn't work for me. The import statement fails with an error message such as: error: object jai is not a member of package com.sun.media The class in question is definitely in one of the jars, I checked.

viktortnk Over a year ago

Hm. I don't know. It just works for me. I have checked with some jar

Marcus Downing · Accepted Answer · 2011-12-01 09:21:45Z

10

For some reason, the glob (*.jar) wasn't working. I was able to get the script running by putting in all the libraries by hand:

#!/bin/sh
exec scala -cp lib/jai_codec.jar:lib/jai_core.jar:lib/mlibwrapper_jai.jar $0 $@
!#

import javax.media.jai.{JAI, RenderedOp}

I don't know why the glob isn't working though.

Note that in this case I don't have the . in the classpath because the script itself is provided as an argument. In many cases though you will need to include it:

exec scala -cp .:lib/jai_codec.jar:lib/jai_core.jar:lib/mlibwrapper_jai.jar $0 $@

Based on this helpful post, I have a script header that pulls in every jar in a lib folder, even if the script (or the folder it's in) are symlinks.

#!/bin/sh
L=`readlink -f $0`
L=`dirname $L`/lib
cp=`echo $L/*.jar|sed 's/ /:/g'`
/usr/bin/env scala -classpath $cp $0 $@
exit
!#

The first line turns the given script location $0 into its actual location on disk, expanding symlinks.
The second line removes the script name and adds /lib
The third line creates a cp variable with all the jars separated by :
The fourth line runs scala, wherever it may be.
The fifth line exits. This probably isn't necessary, but it makes me feel better.

edited Dec 1, 2011 at 9:21

answered Nov 28, 2011 at 9:23

Marcus Downing

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2 Comments

Noel Yap Over a year ago

Shell globs work only when they match file names. This won't work in a path since ':' is a valid filename character. Also, when globs do match, they'll output a space-separated list of filenames.

Fernando Correia Over a year ago

Add the -savecompiled compiled option to make the script execute faster after the 1st time.

Daniel C. Sobral · Accepted Answer · 2011-11-25 02:07:34Z

4

I recommend you use SBT instead to handle it. See the scripts wiki, which explains how to do something like this:

#!/usr/bin/env scalas
!#

/***
scalaVersion := "2.9.0-1"

libraryDependencies ++= Seq(
  "net.databinder" %% "dispatch-twitter" % "0.8.3",
  "net.databinder" %% "dispatch-http" % "0.8.3"
)
*/

import dispatch.{ json, Http, Request }
import dispatch.twitter.Search
import json.{ Js, JsObject }

def process(param: JsObject) = {
  val Search.text(txt)        = param
  val Search.from_user(usr)   = param
  val Search.created_at(time) = param

  "(" + time + ")" + usr + ": " + txt
}

Http.x((Search("#scala") lang "en") ~> (_ map process foreach println))

answered Nov 25, 2011 at 2:07

Daniel C. Sobral

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5 Comments

Mohamed Ragab Over a year ago

This works but it makes it makes running the simplest script take about 8 seconds, every time, any way around that to make it faster even in subsequent runs?

Daniel C. Sobral Over a year ago

@MohamedRagab I think it can save up on some of the work done, but I'm not sure. A hot JVM is probably more important, such as you can get with Nailgun.

Mohamed Ragab Over a year ago

@DanielCSobral sure Nailgun would help, to my understanding the overhead of starting the JVM is below half a second, and SBT caching saves a bit more time of course. It would be great if some of the processing done here is avoided if not needed, I am playing with an attempt to check first in the bash script the existence of the JAR files in the ivy cache and then adding them to the classpath directly

0fnt Over a year ago

@MohamedRagab Did you make any progress? Is there a way to start SCALA repl backed with .jars inside ivy2 cache?

Mohamed Ragab Over a year ago

A few years later, Ammonite offers a comprehensive solution for writing Scala scripts

M. Modugno · Accepted Answer · 2016-01-29 07:24:46Z

2

To avoid to define classpath definition in every header you can define a function that wraps your scala executable in (for example) your .bashrc and make it visibile to outer scope:

...
function scala() {

    PARAMS=( "$@" )

    FILENAME=${PARAMS[0]}
    REMAINING_PARAMS=(${PARAMS[@]:1:${#PARAMS[@]}})

    CUSTOM_CLASSPATH_DEF=".:/whatever/*"
    /path/to/scala -cp "$CUSTOM_CLASSPATH_DEF" -Dscala.color=true "$FILENAME" "${REMAINING_PARAMS[@]}"
}

export -f scala 
...

Now you can define your header as:

#!/bin/bash
scala "$0" "$@"
exit 0
!#

(You can still use REPL typing 'scala' from command line)

answered Jan 29, 2016 at 7:24

M. Modugno

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Comments

Saber · Accepted Answer · 2012-06-26 04:03:50Z

1

http://www.scalaclass.com/node/10 This should work for you. I just fix the dependency according to it.

answered Jun 26, 2012 at 4:03

Saber

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Comments

user977208 · Accepted Answer · 2015-03-25 20:19:13Z

0

You could also put single quotes around the classpath with a glob, like this:

exec scala -classpath '.:*.jar' "$0" "$@"

answered Mar 25, 2015 at 20:19

user977208

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Comments

Changyi Gu · Accepted Answer · 2019-10-28 22:11:20Z

0

The following works for me on Cygwin

#!/bin/sh

me=`basename "$0"`

exec scala "$me" "$@"

!#

  ...

answered Oct 28, 2019 at 22:11

Changyi Gu

1

2 Comments

WestCoastProjects Over a year ago

This does not answer the question about jars on the classpath

Changyi Gu Over a year ago

This actually helped me to find those jars. Otherwise if I just do exec scala "$0" "$@", I will get an error message like "No such file or class on classpath".

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