Running a grep command using java Runtime api

Question

I need to grep some text inside a list of files(file count is huge) in unix server and then list the file name in a web gui. So I decided best way to achieve this is by writing a unix command executer using Runtime.getRuntime(). Works fine for most of the unix command but facing this strange grep issue.

First of all code:

public class UnixCommandExecutor {

    private static StringBuffer output = new StringBuffer();

    public static String exec(String command) throws Exception{
        Process process = null;
        process = Runtime.getRuntime().exec(command);
        BufferedReader stdErr = getBufferedReader(process.getErrorStream());
        BufferedReader stdIn = getBufferedReader(process.getInputStream());
        StringBuffer data = extractData(stdErr);
        if (data.length() >= 1) {
            System.out.println("Error: " +data.toString());
            throw new Exception(data.toString());
        }
        data = extractData(stdIn);
        if (data.length() >= 1) {
            output = data;
            System.out.println("Output: " +data.toString());
        }
        return output.toString();
    }

    private static BufferedReader getBufferedReader(InputStream stream) {
        InputStreamReader inReader = new InputStreamReader(stream);
        BufferedReader buffReader = new BufferedReader(inReader);
        return buffReader;
    }

    private static StringBuffer extractData(BufferedReader reader)
            throws IOException {
        StringBuffer data = new StringBuffer();
        String s = "";
        while ((s = reader.readLine()) != null) {
            data.append(s + "\n");
        }
        return data;
    }

    public StringBuffer getOutput() {
        return output;
    }
}

Now the call would be something like this: String output = exec("find . -name blah"); This works fine and the result is perfect. Or any other unix command executes and provides the result properly.

But when grep command is used it gives a strange error: String output = exec("grep -l executor *");

Error: grep: *: No such file or directory

This is strange, since if I run this command directly on unix it gives the desired result. Also tried giving the file path something like, String output = exec("grep -l executor /file/path/*"); even then the error is:

Error: grep: /file/path/*: No such file or directory

Any ideas? or any other better way to solve this? Any suggestion is welcome.

ok.. i got this to work. Basically i needed two thing to make it to work. First use /bin/sh -c and secondly use Runtime.exec(String[]) api. So overall my method call now looks like String[] commands = new String[]{"/bin/sh","-c","grep -l executor *"}; exec(commands); Works just fine and result is displayed — A.K
– A.K, Commented Jan 2, 2014 at 7:33

Sibbo · Accepted Answer · 2014-01-02 15:27:35Z

0

The * is interpreted by the shell, not grep itself. So it doesn't work if you start grep from your Java program.

You can use grep with -r to make it search recursively, then use . for the current directory:

grep -lr executor .

To simulate the behaviour of the shell, just replace * with a space separated list of all files in the folder you want to search in. You can get the list of all files with:

StringBuilder str = new StringBuilder();

for (File f : new File("your folder").listFiles()) {
    if (f.isFile()) {
        str.append(' ').append(f.getPath());
    }
}

Now just replace the * with the result of str.toString().

edited Jan 2, 2014 at 15:27

answered Jan 2, 2014 at 4:42

Sibbo

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1 Comment

A.K Over a year ago

I guess you are bang on that * is interprestted by shell and thats why I am facing this problem. But to use grep . and recursivly is expensive and impacts on performance as it will include unwanted files to grep whic I would like to avoid. On other note, what would be the best way to tackle * in grep? any ideas?

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