Java cannot execute system command (Ubuntu)

Question

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?

raphaëλ · Accepted Answer · 2012-05-19 13:16:58Z

4

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();

answered May 19, 2012 at 13:16

raphaëλ

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2 Comments

raphaëλ Over a year ago

Because you have to actually run "bash" (or "sh"), which is the interpreter. And you pass in the command you would like to execute (for bash this is passed using the -c option)

Rob Kielty Over a year ago

@Pantelis your original code would have worked if the file that you passed to the ProcessBuilder ctr was an executable file. As it was the shell script runCalculator.sh a shell (bash or sh) is the executable program file required to interpret the shell script commands and run them. At the command line run $file /usr/bin/bash and compare the output to running $file ./runCalculator.sh

Hovercraft Full Of Eels · Accepted Answer · 2012-05-19 13:14:32Z

3

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

answered May 19, 2012 at 13:14

Hovercraft Full Of Eels

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Comments

Hakan Serce · Accepted Answer · 2012-05-19 13:15:28Z

3

Try this:

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

answered May 19, 2012 at 13:15

Hakan Serce

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Comments

Bosko Mijin · Accepted Answer · 2013-10-28 16:18:33Z

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).

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