Executing shell commands from Scala REPL - scala

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 ?

Answer 1

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".!

Answer 2

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

Answer 3

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)

Answer 4

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.

Answer 5

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