Grep output to file (Java)

Question

How can I store the output of a grep in a file using Java?

I'm using Runtime and Process to execute the grep, then I read the InputStream

BufferedReader stdInput = new BufferedReader(new InputStreamReader(pr.getInputStream()));

and now I'd like to store the content of the grep in a file, but I'm getting an empty file.

With

String s = null;
while ((s = stdInput.readLine()) != null) {
    System.out.println(s);
}

I am correctly seeing the grep's output. However, when I try to write it to a file, the file is empty.

PrintWriter writer = null;
writer = new PrintWriter("grep__output", "UTF-8");
writer.println(s);
writer.close();

Also, I tried to directly writing to file in the above while (previously creating the file), but it's the same.

grep was just an example. I'm interested in any bash tool basically. — user1351781
– user1351781, Commented Apr 1, 2014 at 21:27

Alcanzar · Accepted Answer · 2014-04-01 20:55:56Z

1

You need to have the println in the loop that's reading. You are likely just writing null to the file.

PrintWriter writer = new PrintWriter("grep__output", "UTF-8");
String s = null;
while ((s = stdInput.readLine()) != null) {
   writer.println(s);
} 
writer.close();

answered Apr 1, 2014 at 20:55

Alcanzar

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1 Comment

user1351781 Over a year ago

OMG, it's working now. I swear I tried exactly this same code, in fact, read my last sentence in the question xD.

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