Develop Reference

Shell command via ProcessBuilder fails to do anything on MacOS, but exit code == 0 and no errors

So I have been trying to find a solution to this problem for quite a while now but haven't been able to even get an error message. I am trying to toggle the dark mode on MacOS with this command: /usr/local/bin/dark-mode on
It works if I execute it with the standard terminal, but executing the code below doesn't do anything. The log file is empty. To make sure my code is correct I used a different command (commented out) and this one gave me the correct output to whoami and returned my current user.
I thought this may have to do with application security on MacOS? I have no idea where to start though.
private void switchDark() {
try {
//Activate the dark mode on MacOS
String command = new String[] { "/usr/local/bin/dark-mode", "on" };
//String command = new String[] { "whoami" }; //This works and gives me the current user
ProcessBuilder pb =
new ProcessBuilder(command[0], command[1]);
File log = new File("LOG.txt");
pb.redirectErrorStream(true);
pb.redirectOutput(Redirect.appendTo(log));
Process proc = pb.start();
proc.waitFor();
if(proc.exitValue() != 0) {
throw new IllegalThreadStateException();
}
} catch (IOException | InterruptedException | IllegalThreadStateException ex) {
System.out.println("Setting dark mode failed!");
if(debug)System.out.println(ex.getMessage());
}
}

I looked at the code to see what that "dark-mode" command does. (https://github.com/sindresorhus/dark-mode - thanks #MadProgrammer)
I'm no Swift or MacOS expert, but that command's implementation doesn't look like it tests if the AppleScript command succeeded. Furthermore, there doesn't seem to be anything to set non-zero exit status in the event of a failure.
So my conclusion is that the underlying AppleScript command is not working ... for reasons that are not reported ... and that information is not passed back to Java via the exit status. There is nothing you can do about it at the Java level.
My guess is that the "dark mode" request is actually failing for permissions-related reasons.

How to Run a jar from another jar and show the console output from the first runnable during the execution

I'm running a jar file from another jar like here somebody answers but waiting for the process.
Process proc = Runtime.getRuntime().exec("java -jar A.jar" + stringParams);
try {
proc.waitFor();
} catch (InterruptedException e) {
e.printStackTrace();
}
InputStream in = proc.getInputStream();
InputStream err = proc.getErrorStream();
My problem comes when i have no feedback on the status of the program that is called, but i don't want my program continues beyond those lines. I would need the standard and error outputs but the results are shown when the execution is over. Is there any way of executing and getting those streams while the jar is still running?

Buffered/unbuffered
It seems like an issue with buffered output.
Executed process (in this case java -jar <path>) buffers output and writes it only when it's done (in big chunks, we don't like that!)
So one way to go is execute process through unbuffering (very hacky tools):
unbuffered <command>
stdbuf -i0 -o0 -e0 <command>
use terminal emulation
Hacking
stdbuf is part of GNU tools.
https://www.gnu.org/software/coreutils/manual/html_node/stdbuf-invocation.html
unbuffered is part of expect package.
https://wiki.tcl.tk/3548
The key thing is making the program thinking that it's in interactive mode (like you are launching it from console).
The first two options are very hacky and do not work in all cases (idk if java command works with them?)
Emulation
The third option is most promising.
We launch a program (terminal emulator) that emulates interactive terminal making program think it's working in real active session!
Pty4j
You might use pty4j too:
From there: https://github.com/traff/pty4j
// The command to run in a PTY...
String[] cmd = { "java", "-jar", "path_to_jar" };
// The initial environment to pass to the PTY child process...
String[] env = { "TERM=xterm" };
PtyProcess pty = PtyProcess.exec(cmd, env);
OutputStream os = pty.getOutputStream();
InputStream is = pty.getInputStream();
// ... work with the streams ...
// wait until the PTY child process terminates...
int result = pty.waitFor();
// free up resources.
pty.close();
Zt-exec
Maybe it's worth trying zt-exec?
I have no idea how it executes commands.
But it may be it (I didn't test that).
Using https://github.com/zeroturnaround/zt-exec
new ProcessExecutor().command("java", "-jar path_to_jar")
.redirectOutput(new LogOutputStream() {
#Override
protected void processLine(String line) {
...
}
})
.execute();
That should work, but I didn't test that.
In general, there are no ways to nicely resolve your problem.
Depending on what platforms you want to target consider using unbuffered, stdbuff or the (slowest) terminal emulation...
Please let me know if that helps and good luck! :)

cmd.exe is hanging unexpectedly depending on where the file I use is located

This has got to be one of the strangest things I have ever observed. Consider the following Java program:
import java.io.IOException;
public class StrangeError {
public static void main(String[] args) {
try {
Process process = new ProcessBuilder(
"cmd",
"/c",
"\"C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\vcvarsall.bat\" amd64 && set"
).start();
process.waitFor();
} catch (IOException|InterruptedException e) {
System.out.println(e.getMessage());
}
}
}
I compiled it with javac StrangeError.java, copied it to my server running Windows Server 2012 R2, and ran it with java StrangeError.
Here's where things start to get weird. The program hangs, waiting for the process it spawned to finish. This is not the expected behavior, since the vcvarsall.bat script should complete immediately as well as set.
So I started playing around and discovered the following:
Removing set causes vcvarsall.bat to terminate
Removing vcvarsall.bat causes set to terminate
Replacing && with || causes everything to terminate correctly
Copying vcvarsall.bat to a location on the desktop and changing the path causes everything to terminate correctly
A nearly equivalent program works fine in Go using the same commands
I get this output if I run everything in WinDbg and interrupt the process after it hangs
This does not appear to be reproducible with vcvarsall.bat from MSVC2013 but is also reproducible with MSVC2015 on Windows 10
What on earth is wrong with the original program? If I copy and paste the entire command (cmd /c "C:\...) into Start->Run, it immediately launches cmd and terminates, as expected.
Is this a bug with Java? Is this a bug with Windows?

Is this a bug with Java? Is this a bug with Windows?
It's a bug in your code. :-)
By default, a child process created using a ProcessBuilder object has output redirected to a pipe, the parent end of which can be obtained using Process.getInputStream() and which is not automatically drained if your code does not make use of it.
Since your code simply calls .waitFor without making any provision to drain the pipe, it will deadlock as soon as the pipe's buffer overflows. I believe the default buffer size is 4,096 bytes. On my machine, the output of the command you're running is 5,192 bytes, but this will vary depending on the original contents of the environment block. (From the sounds of it, the output length in your environment is borderline, only just above the limit, so that even small changes like changing the version of VS make a difference.)
One of the many possible solutions, depending on what you're actually trying to do, is to tell Java not to pipe the child's output:
import java.io.IOException;
public class StrangeError {
public static void main(String[] args) {
try {
ProcessBuilder processb = new ProcessBuilder(
"cmd",
"/c",
"\"C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\vcvarsall.bat\" amd64 && set"
);
processb.redirectOutput(ProcessBuilder.Redirect.INHERIT);
Process process = processb.start();
process.waitFor();
} catch (IOException|InterruptedException e) {
System.out.println(e.getMessage());
}
}
}

Not possible to read standard input and output error inside the same ProcessBuilder.
So you need to create two ProcessBuilder
Process process1 = new ProcessBuilder(
"cmd",
"/c",
"\"C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\vcvarsall.bat\",
"amd64");
Process process2 = new ProcessBuilder(
"cmd",
"/c",
"set");
process1.start();
if (process1.waitFor() == 0) {
process2.start();
if (process2.waitFor() == 0) {
// Successfull execution
}
}
And one thing : I don't think it is a good practice to do shell/batch launches with Java (or another language). Maybe you should use a script (shell, batch, python, perl...) to control standard input/output streams.

Java cannot execute system command (Ubuntu)

It's not the first time I have tried to execute a system command from Java; but this time it turns out to be very hard. I have a script that executes just fine from the terminal. It reads input from a file (input.txt), it processes it and exports the result in another file (ouput.txt). The whole thing lasts no more than 1sec. But, when I try to execute it from Java, it gets stuck and never finishes. This is my code:
Process p = new ProcessBuilder("./runCalculator.sh").start();
p.waitFor();
I have also tried with Runtime.getRuntime().exec("./runCalculator.sh") but all the same. I've read both the InputStream and the ErrorStream of the process. The error stream returns nothing but a message like "Starting Calculation..."
Any ideas?

You need to use the following code:
ProcessBuilder pb = new ProcessBuilder();
pb.command("bash", "-c", "./runCalculator.sh");
Process process = pb.start();
int retValue = process.waitFor();

You likely need to invoke the unix command interpreter/processor for this to work. Please see: When Runtime.exec() won't.

Try this:
Process p = new ProcessBuilder("sh ./runCalculator.sh").start();

Another, simplier solution is that you can open program by entering the name of the program (this assumes that program is installed) instead of creating script and calling it.
Note that the name of the program isn't always what you see in Gnome's menu, for example Gnome's calculator is "gnome-calculator". Regarding this facts, you can run calculator by the folowing line:
Process p = Runtime.getRuntime().exec("gnome-calculator");
In that case you don't have a need for any sh scripts (in your case runCalculator.sh).

Runtime.getRunTime().exec not behaving like C language "system()" command

In "C", I can run a long blocking process in the background (AND HAVE IT CONTINUE TO RUN) after the starting process has exited.
void main(void)
{
system("some_long_blocking_process &");
exit();
}
// "some_long_blocking_process" is still running here (DESIRED BEHAVIOR)
Java's getRuntime().exec() DOESN'T have this behavior. Instead, "some_long_blocking_process" ends immediately when the Java process ends.
Anyone know how I can recapture this behavior in Java?
I am using Java 1.4 (No process builder)
I specifically am looking to start the long blocking process and to exit immediately (no "waitFor(), etc.)
Things I have already tried (the process runs correctly, but I still get the same undesired behavior)
adding "nohup" and run in foreground ("nohup some_long_process")
adding "nohup" and running in background ("nohup some_long_process &")
run in foreground ("some_long_process")
run in background ("some_long_process &")
THANKS!
Thanks to all the suggestions... I've decided to use jtahlborn's answer (it worked for me)

try this:
String[] cmd = {"/bin/sh", "-c", "yourcommand args"};
Process p = Runtime.getRuntime().exec(cmd);
when redirect stream to /dev/null:
String[] cmd = {"/bin/sh", "-c", "yourcommand args > /dev/null 2>&1 &"};
Process p = Runtime.getRuntime().exec(cmd);

the only way we were able to achieve this with java was to add another layer of script. you need a simple wrapper script which invokes the app you actually want to run, e.g.:
runner.sh:
#!/bin/sh
nohup "$#" > /dev/null 2>&1 &
then invoke "/bin/sh runner.sh the real command" from your java program.

EDIT:
Have your tried this?
Runtime.getRuntime().exec("/bin/sh -c /usr/X11/bin/xterm &")
This worked for me on MacOS.
Previous answer (JDK 1.5, apologies for not reading the question correctly):
To execute a process without waiting you can use the ProcessBuilder
ProcessBuilder pb = new ProcessBuilder("/usr/X11/bin/xterm");
pb.start();

Your problem is probably due to the trailing &. Try removing it.
getRuntime().exec() is more similar to fork() and exec() than system().
system() passes the command to the shell, and it's Bash that understands that the trailing ampersand means to run the process in the background.
getRuntime().exec() parses the command using a StringTokenizer to parse the command, and doesn't do anything with the trailing ampersand. That's simply passed as the first argument to your some_long_blocking_process, which may exit out immediately on the unknown error.

Have you tried spawning a new Thread to run the executable? Try:
new Thread(new Runnable() {
#Override
public void run() {
try {
Runtime.getRuntime().exec(<your exec>);
} catch (IOException e) {
e.printStackTrace();
}
}
}).run();
This way, the main process won't shutdown until the exec has finished running (and the thread has finished).
Also, don't manually call exit() in your application unless you have some overwhelming reason to--the JVM does a good job of detecting when the application has finished on its own. This way, you won't force close threads that are running in the background.