Error while trying to get Unix file Permissions in Java6

Question

I want to read file permissions in unix and write the permissions to a csv file. Here is my code:

           static void getFilePermissions(String fileName) {

    try {
        Process proc = Runtime.getRuntime().exec("ls -lrt "+fileName + "| cut -c1-10");
        BufferedReader in = new BufferedReader(new InputStreamReader(
                proc.getInputStream()));
        String line = null;
        while ((line = in.readLine()) != null) {
            System.out.println(line);
        }
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

public static void main(String[] args) {
    // getRecursiveFiles("/scratch/samaggar/SampleDir");
    getFilePermissions("/scratch/samaggar/SampleDir");
}

It gives me the IOException Kindly suggest.I can't use Java7 which provides built in mechanism.

What's the stack trace? (You should also use the version of exec() that takes an array to pass the parameters in.) — Michael Berry
– Michael Berry, Commented Feb 26, 2014 at 11:57

fge · Accepted Answer · 2014-02-26 11:59:04Z

3

Your problem starts here:

"ls -lrt "+fileName + "| cut -c1-10"

Runtime.exec() does NOT launch a shell, and therefore | is treated as an argument to your ls command. ALso, consider what will happen if the file name has a space in it.

Your second problem: you use Runtime.exec(); don't. Use a ProcessBuilder. It has very nifty methods for output redirections etc etc.

Your third problem: instead of piping through cut, just use Java's string methods to do that; it will be faster (no need to fork() for one).

Finally: have a look at the stat command and its --format option...

answered Feb 26, 2014 at 11:59

fge

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1 Comment

Sammidbest Over a year ago

Thanks for your valuable suggestions.I am checking ProcessBuilder.In the meanwhile,I removed the cut command and used Java's string methods.Its working!!

Bimalesh Jha · Accepted Answer · 2014-02-26 12:06:40Z

0

The problem is already identified in the earlier answer- piping (|) to cut will not work from Runtime.exec(). Instead create a simple shell script e.g. get_perm.sh and put all your scripting code inside that shell script, then call this script from Runtime.exec(). It should work.

answered Feb 26, 2014 at 12:06

Bimalesh Jha

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