Executing shell commands from Scala REPL

Question

An interesting feature of Scala REPL is if you drop any jar in your %SCALA_HOME%\lib directory, it is available for import from the REPL. I have several jars there, and I often need to find out which ones are available to be included. So I always have to open another command window and find out which jars exist in that directory. It would be great if the REPL allowed me to execute system commands such as dir or ls or at least list all the jars in the above lib directory. What is the easiest way (if any) to invoke shell commands in REPL ?

Community · Accepted Answer · 2017-05-23 10:31:15Z

24

In REPL the :sh command allow you to introduce shell command:

Windows version:

scala> :sh cmd /C dir
  res0: scala.tools.nsc.interpreter.ProcessResult = `cmd /C dir` (28 lines, exit 0)
scala> res0 foreach println

(unfortunately, there is no way to avoid the call to cmd \C before the shell command)

Unix-like version:

scala> :sh ls
  res0: scala.tools.nsc.interpreter.ProcessResult = `cmd /C dir` (28 lines, exit 0)
scala> res0 foreach println

Update: Inspired by Daniel's answer, a little trick for windows user:

scala> implicit def stringToDosProcess(s: String) =
  scala.sys.process.stringToProcess("cmd /C "+ s)
stringToDosProcess: (s: String)scala.sys.process.ProcessBuilder

scala> "dir".!

edited May 23, 2017 at 10:31

CommunityBot

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answered Mar 27, 2012 at 9:44

Nicolas

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4 Comments

Jus12 Over a year ago

Thanks! this is closest to what I was looking for.

Hossein Over a year ago

Doesn't work for me on Windows: Welcome to Scala 2.11.8 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_121). Type in expressions for evaluation. Or try :help.

scala scala> :sh cmd /C dir  res0: scala.tools.nsc.interpreter.ProcessResult = `cmd /C dir` (27 lines, exit 0)   scala> res0 foreach println  <console>:13: error: value foreach is not a member of scala.tools.nsc.interpreter.ProcessResult        res0 foreach println             ^

Amey Joshi Over a year ago

Try res0.lines foreach println.

user unknown Over a year ago

toDos, haha! :)

Daniel C. Sobral · Accepted Answer · 2012-03-27 18:25:06Z

18

Alternative: use Scala's sys.process library:

scala> import sys.process._
import sys.process._

scala> "ls /home/dcs/scala-2.9.1.final".!
bin
doc
lib
man
meta
misc
src
res1: Int = 0

answered Mar 27, 2012 at 18:25

Daniel C. Sobral

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5 Comments

Jus12 Over a year ago

cool but not so great in windows, as "dir", etc (and most useful commands) are not separate files but embedded in the shell interpretter.

Nicolas Over a year ago

I've updated my answer to build something as tasty as this for windows users

Daniel C. Sobral Over a year ago

@Jus12 Use cmd for them. The question was about executing shell commands from REPL, the actual problem was listing files. I gave one solution for each. :-)

Jus12 Over a year ago

Yes I agree. The problem is with Windows. Both your answers are very useful though.

Erik Kaplun Over a year ago

looks like for non-builtin commands you have to use Seq("cmdname", "arg1", "arg2") to be able to pass in arguments.

jwvh · Accepted Answer · 2016-09-18 02:42:35Z

6

UPDATE

The means for extracting :sh output has changed over the years.

Welcome to Scala 2.11.8 (OpenJDK 64-Bit Server VM, Java 1.8.0_91).
Type in expressions for evaluation. Or try :help.

scala> :sh date
res0: scala.tools.nsc.interpreter.ProcessResult = `date` (1 lines, exit 0)

scala> res0 foreach println
<console>:13: error: value foreach is not a member of scala.tools.nsc.interpreter.ProcessResult
       res0 foreach println
            ^

scala> res0.show
<console>:13: error: value show is not a member of scala.tools.nsc.interpreter.ProcessResult
       res0.show
            ^

scala> res0.lines
res3: List[String] = List(Sat Sep 17 19:29:26 PDT 2016)

answered Sep 18, 2016 at 2:42

jwvh

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Comments

Soheil Pourbafrani · Accepted Answer · 2019-02-12 12:58:44Z

3

Here is a little-known trick of REPL:

Welcome to Scala version 2.10.0-20120323-101508-45eebcf98d (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_26).
Type in expressions to have them evaluated.
Type :help for more information.

scala> /home/dcs/scala-2.9.1.final/<TAB>
/home/dcs/scala-2.9.1.final/misc   /home/dcs/scala-2.9.1.final/bin    /home/dcs/scala-2.9.1.final/man    /home/dcs/scala-2.9.1.final/src    /home/dcs/scala-2.9.1.final/lib    
/home/dcs/scala-2.9.1.final/meta   /home/dcs/scala-2.9.1.final/doc    

scala> /home/dcs/scala-2.9.1.final/lib/<TAB>
/home/dcs/scala-2.9.1.final/lib/scala-dbc.jar        /home/dcs/scala-2.9.1.final/lib/scala-swing.jar      /home/dcs/scala-2.9.1.final/lib/jline.jar            
/home/dcs/scala-2.9.1.final/lib/scala-library.jar    /home/dcs/scala-2.9.1.final/lib/scala-compiler.jar   /home/dcs/scala-2.9.1.final/lib/scalap.jar           

scala> /home/dcs/scala-2.9.1.final/lib/scala-library.jar
res0: scala.tools.nsc.io.File = /home/dcs/scala-2.9.1.final/lib/scala-library.jar

Where <TAB> is I pressing tab.

edited Feb 12, 2019 at 12:58

Soheil Pourbafrani

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answered Mar 27, 2012 at 18:23

Daniel C. Sobral

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1 Comment

virtualeyes Over a year ago

you can REPL insert <TAB> everywhere, "/ho<TAB>/dcs/scala-2.9<TAB>", or at least on Linux that's the case

clemens · Accepted Answer · 2018-01-16 06:54:14Z

UPDATE 2018/01/15

Example: you like to see the files in the current working directory:

scala> :sh ls -l
res3: scala.tools.nsc.interpreter.ProcessResult = `ls -l` (13 lines, exit 0)

But you can't do this:

scala> res3.foreach {println}
<console>:40: error: value foreach is not a member of scala.tools.nsc.interpreter.ProcessResult
       res3.foreach {println}
            ^

First you have to assign the lines to another type that supports iteration:

scala> res3.lines
res7: List[String] = List(total 960, -rw-r--r--@  1 dave  staff   11325 Jan  3 15:01 LICENSE, -rw-r--r--@  1 dave  staff    8859 Jan  3 15:01 README.rst, drwxr-xr-x@  3 dave  staff      96 Jan  3 15:03 assembly, drwxr-xr-x@ 20 dave  staff     640 Jan  3 15:01 bin, drwxr-xr-x@ 13 dave  staff     416 Jan  3 15:01 doc, drwxr-xr-x@  7 dave  staff     224 Jan  3 15:01 docker, drwxr-xr-x@  6 dave  staff     192 Jan  3 15:03 examples, -rw-r--r--@  1 dave  staff     826 Jan  3 15:01 gradle.properties, -rw-r--r--@  1 dave  staff     128 Jan  3 15:04 h2o_drivers.txt, drwxr-xr-x   3 dave  staff      96 Jan 16 00:54 h2ologs, drwxr-xr-x@  5 dave  staff     160 Jan  3 15:04 py, -rw-r--r--@  1 dave  staff  455890 Sep 19 04:18 rsparkling.tar.gz)

Then iterate, and voila!

scala> res7.foreach {println}
total 960
-rw-r--r--@  1 dave  staff   11325 Jan  3 15:01 LICENSE
-rw-r--r--@  1 dave  staff    8859 Jan  3 15:01 README.rst
drwxr-xr-x@  3 dave  staff      96 Jan  3 15:03 assembly
drwxr-xr-x@ 20 dave  staff     640 Jan  3 15:01 bin
drwxr-xr-x@ 13 dave  staff     416 Jan  3 15:01 doc
drwxr-xr-x@  7 dave  staff     224 Jan  3 15:01 docker
drwxr-xr-x@  6 dave  staff     192 Jan  3 15:03 examples
-rw-r--r--@  1 dave  staff     826 Jan  3 15:01 gradle.properties
-rw-r--r--@  1 dave  staff     128 Jan  3 15:04 h2o_drivers.txt
drwxr-xr-x   3 dave  staff      96 Jan 16 00:54 h2ologs
drwxr-xr-x@  5 dave  staff     160 Jan  3 15:04 py
-rw-r--r--@  1 dave  staff  455890 Sep 19 04:18 rsparkling.tar.gz

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