Platform-independent way to start program on PATH?

Question

Is there a platform-independent way in Java to start an external process that executes program which it finds using the system path?

It should work at least on Windows, Linux and Mac.

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Normally your have to give the full path to an executable file, like this:

new ProcessBuilder("/some/path/execfile", "arg").start();

It is possible to start a program that is on the system path by starting a shell:

new ProcessBuilder("/bin/bash", "-c", "execfile", "arg").start();

But this is not portable between OS:s. (This is the solution that is given to this question.)

Answer 1

ProcessBuilder does use the $PATH.

import java.io.*;

public class ProcessBuilderTest {
    public static void main(String... args) throws Exception {
        ProcessBuilder pb = new ProcessBuilder(args);
        pb.redirectErrorStream(true);
        Process p = pb.start();
        int exitCode = p.waitFor();
        printStream(p.getInputStream());
        printStream(p.getErrorStream());
        System.out.println("Exit code: " + exitCode);
    }

    static void printStream(InputStream stream) throws IOException {
        try (BufferedReader br = new BufferedReader(new InputStreamReader(stream))) {
            String line;
            while ((line = br.readLine()) != null) {
                System.out.println(line);
            }
        }
    }
}

Running this on MacOS:

robert@mac:~$ java ProcessBuilderTest.java ls *.java
ProcessBuilderTest.java
Exit code: 0
robert@mac:~$ java ProcessBuilderTest.java ls *.class
ls: cannot access '*.class': No such file or directory
Exit code: 2
robert@mac:~$ java ProcessBuilderTest.java which ls
/usr/local/opt/coreutils/libexec/gnubin/ls
Exit code: 0
robert@mac:~$

Same on Linux:

robert@linux:~$ java ProcessBuilderTest.java ls *.java
ProcessBuilderTest.java
Exit code: 0
robert@linux:~$ java ProcessBuilderTest.java ls  *.class
ls: cannot access '*.class': No such file or directory
Exit code: 2
robert@linux:~$ java ProcessBuilderTest.java which ls
/usr/bin/ls
Exit code: 0
robert@linux:~$

I don't use Windows, so cannot test on that.