Alternative to java.lang.Runtime.exec() that can execute command lines as a single string?

Question

I am calling java.lang.Runtime.exec(...) but this seems to accept the command lines as an array and I want to use a single string.

How can I do the same using a single string?

There is a `Runtime.exec(String command)` method, see your link. And everyone who uses `Runtime.exec(...)` should read this: http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html — Peter Bagyinszki, Jun 01 '12 at 16:55
@PeterBagyinszki Thank! Now the only problem is that I do want to setup the current directory and still run it as a single command. — sorin, Jun 01 '12 at 16:58
There is a method for that too: `exec(String command, String[] envp, File dir)` — Peter Bagyinszki, Jun 01 '12 at 17:13
This is exactly what I am doing not and Java is complaining that it cannot find `python`. The command line executed is something like `python file ....` and envp is `null`, and obviously python is installed (linux) and also in `PATH`. — sorin, Jun 01 '12 at 17:46

score 2 · Answer 1 · answered Jun 01 '12 at 16:09

From the linked Javadocs:

envp - array of strings, each element of which has environment variable settings in the format name=value, or null if the subprocess should inherit the environment of the current process.

So just pass in null for the second parameter, and the environment will be inhereted.

Peter Bagyinszki · Answer 2 · 2012-06-01T18:05:54.373

If you pass null for the second paramter the current environment will be inherited.

If you want to modify the current environment, you can build it from System.getEnv() like this:

private static String[] getEnv() {
    Map<String, String> env = System.getenv();
    String[] envp = new String[env.size()];
    int i = 0;
    for (Map.Entry<String, String> e : env.entrySet()) {
        envp[i++] = e.getKey() + "=" + e.getValue();
    }
    return envp;
}

Update

You can check your Java path with System.out.println(System.getenv("PATH"));

If path is ok, then try it with

String[] commands = new String[] { "bash", "-c", "python foo/bar.py" };
Runtime.getRuntime().exec(commands, null, new File("/workingDir"));

score 1 · Answer 3 · answered Jun 01 '12 at 16:09

From the documentation:

envp - array of strings, each element of which has environment variable settings in the format name=value, or null if the subprocess should inherit the environment of the current process.

It sounds like you want to pass null for that argument.

score 0 · Accepted Answer · answered Jun 14 '12 at 09:25

Currently there is no way of calling a system command with a command line as a single string and be able to specify the current directory.

It seems that Java API is missing this basic feature :)

The workaround is to use the array version instead of string.

Alternative to java.lang.Runtime.exec() that can execute command lines as a single string?

4 Answers4

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