Question

I’m using graphviz to generate graphs based on the messages passed in a scala program.
To invoke the graphviz application from inside the scala program, I’m using the exec() method (similar to Java). It successfully executed the command and created the graph when I used the below code snippet:

var cmd: String = "dot -Tpng Graph.dot -o Graph.png"  
var run: Runtime = Runtime.getRuntime() ;
var pr: Process = run.exec(cmd) ;

However It fails to execute after changing the path of the input and output files (I just included a directory inside which the input file and output file resides as shown below)

  def main(args: Array[String]): Unit = {

   var DirectoryName: String = "Logs"

   var GraphFileName: String = DirectoryName + File.separator + "Graph.dot"      
   val GraphFileObj: File = new File(GraphFileName)

   // var cmd: String = "dot -Tpng Graph.dot -o Graph.png" 
   var cmd: String = "dot -Tpng \"" + GraphFileObj.getAbsolutePath + "\" -o \"" + DirectoryName + File.separator + "Graph.png\"" ;
   println(cmd)

   var run: Runtime = Runtime.getRuntime() ;
   var pr: Process = run.exec(cmd) ;

  }

The same command when executed through terminal gives proper output. Can you please help me to find what I’m missing?

Answer 1

exec is not a shell…e.g. quoting won’t work as you expect, and thus your path (which may contain spaces, etc) will not be processed as you expect. The command will be broken apart using StringTokenizer, and your literal quotes will be…well..literal.

Use the form of exec that takes an array instead, so you can tokenize the command correctly.

val args = Array[String]("dot", "-Tpng", GraphFileObj.getAbsolutePath, ...);
run.exec(args)