import java.io.*;

/**
 * Searches the input file (or standard input if no file is given)
 * for lines containing the given pattern and prints these lines.
 * <p>
 * Usage: java Grep PATTERN [FILE]
 * 
 * @author Stefan Nilsson
 * @version 2006.02.23
 */
public class Grep
{
    private static final String NAME = "Grep";
    private static final String USAGE =
        "Usage: java " + NAME + " PATTERN [FILE]";
    private static final String STDIN = "stdin";
    private static final String OPEN_ERR = NAME + ": cannot open ";
    private static final String READ_ERR = NAME + ": error reading ";
    
    private Grep() {}

    /**
     * Searches the input file (argv[1] or standard input if no file
     * is given) for lines containing the given pattern (argv[0]) and
     * prints these lines.
     */
    public static void main(String[] args) {
	if (args.length == 0 || args.length > 2) {
	    System.err.println(USAGE);
            System.exit(1);
	}
	final String PATTERN = args[0];
	final String FILE_NAME = args.length == 1 ? STDIN : args[1];
	BufferedReader in = null;
	try {
	    if (args.length == 1)
	        in = new BufferedReader(new InputStreamReader(System.in));
            else
                in = new BufferedReader(new FileReader(FILE_NAME));
            (new Grep()).search(PATTERN, in);
        } catch (FileNotFoundException e) {
            System.err.println(OPEN_ERR + FILE_NAME);
        } catch (IOException e) {
            System.err.println(READ_ERR + FILE_NAME);
        } finally {
            try {
                if (in != null)
                    in.close();
            } catch (IOException e) {
                // At least we tried.
            }
        }
        System.exit(0);
    }
    
    /** 
     * Prints all lines in the stream that contain the pattern.
     */
    private void search(String pattern, BufferedReader in) throws IOException {
        String line;
        while ((line = in.readLine()) != null)
            if (line.indexOf(pattern) != -1)
                System.out.println(line);
    }
}