How to check existence of a program in the path

Question

I'm writing a program in scala which call:

Runtime.getRuntime().exec( "svn ..." )

I want to check if "svn" is available from the commandline (ie. it is reachable in the PATH). How can I do this ?

PS: My program is designed to be run on windows

Answer 1

Here's a Java 8 solution:

String exec = <executable name>;
boolean existsInPath = Stream.of(System.getenv("PATH").split(Pattern.quote(File.pathSeparator)))
        .map(Paths::get)
        .anyMatch(path -> Files.exists(path.resolve(exec)));

Replace anyMatch(...) with filter(...).findFirst() to get a fully qualified path.

---

Here's a cross-platform static method that compares common executable extensions:

import java.io.File;
import java.nio.file.Paths;
import java.util.stream.Stream;

import static java.io.File.pathSeparator;
import static java.nio.file.Files.isExecutable;
import static java.lang.System.getenv;
import static java.util.regex.Pattern.quote;

public static boolean canExecute( final String exe ) {
  final var paths = getenv( "PATH" ).split( quote( pathSeparator ) );
  return Stream.of( paths ).map( Paths::get ).anyMatch(
    path -> {
      final var p = path.resolve( exe );
      var found = false;

      for( final var extension : EXTENSIONS ) {
        if( isExecutable( Path.of( p.toString() + extension ) ) ) {
          found = true;
          break;
        }
      }

      return found;
    }
  );
}

This should address most of the critiques for the first solution. Aside, iterating over the PATHEXT system environment variable would avoid hard-coding extensions, but comes with its own drawbacks.

Answer 2

I'm no scala programmer, but what I would do in any language, is to execute something like 'svn help' just to check the return code (0 or 1) of the exec method... if it fails the svn is not in the path :P

Runtime rt = Runtime.getRuntime();
Process proc = rt.exec("svn help");
int exitVal = proc.exitValue();

By convention, the value 0 indicates normal termination.