Process.getErrorStream不会捕获所有错误

Question

I use ProcessBuilder to create a Process that runs a script on Linux. I need to check if there were errors while executing this script.

public static String contentInStream(InputStream stream) throws IOException
{
    return contentInReader(new InputStreamReader(stream));
}

public static String contentInReader(Reader reader) throws IOException
{
    BufferedReader br = new BufferedReader(reader);
    String line;
    String content = "";
    while ((line = br.readLine())!=null)
    {
        content += line+"\n";
    }
    return content;
}

public static void execScript(String script)
{
    ProcessBuilder pb = new ProcessBuilder("sh", script);
    Process process = pb.start();
    process.waitFor();
    String errors = contentInStream(process.getErrorStream());
    if (!errors.isEmpty())
    {
        throw new RuntimeException(errors);
    }
}

In a test script I produce two errors, one by explicitly writing to the error channel, and one by trying to write to a file where the script doesn't have write rights.

echo Warning
date > in
>&2 echo Error

The problem is that the string errors only contains "Error", not the error from the command "date > in". The file "in" is not created, as expected. If I try "./testScript.sh > /tmp/std 2> /tmp/err", both errors are in /tmp/err, as expected.

String errors contains: Error

Output when script is run by itself:
/apps/testScript.sh: line 2: in: Permission denied Error

PS: I also tested with the order of the two last lines in the test script reversed. I got the same result, so the error is probably not in contentInReader.

Answer 1

I solved it. Apparently the script was executing in a different directory when it was started from the Java process, where the script has write permissions. So there was no error, and getErrorStream did capture all error output, in this case just "Error".