Another Grep : Grep « Regular Expressions « Java

1. Java
2. Regular Expressions
3. Grep

Another Grep

/*
 * Copyright (c) Ian F. Darwin, http://www.darwinsys.com/, 1996-2002.
 * All rights reserved. Software written by Ian F. Darwin and others.
 * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS''
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 * Java, the Duke mascot, and all variants of Sun's Java "steaming coffee
 * cup" logo are trademarks of Sun Microsystems. Sun's, and James Gosling's,
 * pioneering role in inventing and promulgating (and standardizing) the Java 
 * language and environment is gratefully acknowledged.
 * 
 * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for
 * inventing predecessor languages C and C++ is also gratefully acknowledged.
 */
// Sun Microsystems Example Code @(#)Grep.java 1.1 01/05/10

//Search a list of files for lines that match a given regular-expression
//pattern. Demonstrates NIO mapped byte buffers, charsets, and regular
//expressions.

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.CharBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;

public class GrepSun {

  // Charset and decoder for ISO-8859-15
  private static Charset charset = Charset.forName("ISO-8859-15");

  private static CharsetDecoder decoder = charset.newDecoder();

  // Pattern used to parse lines
  private static Pattern linePattern = Pattern.compile(".*\r?\n");

  // The input pattern that we're looking for
  private static Pattern pattern;

  // Compile the pattern from the command line
  //
  private static void compile(String pat) {
    try {
      pattern = Pattern.compile(pat);
    } catch (PatternSyntaxException x) {
      System.err.println(x.getMessage());
      System.exit(1);
    }
  }

  // Use the linePattern to break the given CharBuffer into lines, applying
  // the input pattern to each line to see if we have a match
  //
  private static void grep(File f, CharBuffer cb) {
    Matcher lm = linePattern.matcher(cb); // Line matcher
    Matcher pm = null; // Pattern matcher
    int lines = 0;
    while (lm.find()) {
      lines++;
      CharSequence cs = lm.group(); // The current line
      if (pm == null)
        pm = pattern.matcher(cs);
      else
        pm.reset(cs);
      if (pm.find())
        System.out.print(f + ":" + lines + ":" + cs);
      if (lm.end() == cb.limit())
        break;
    }
  }

  // Search for occurrences of the input pattern in the given file
  //
  private static void grep(File f) throws IOException {

    // Open the file and then get a channel from the stream
    FileInputStream fis = new FileInputStream(f);
    FileChannel fc = fis.getChannel();

    // Get the file's size and then map it into memory
    int sz = (int) fc.size();
    MappedByteBuffer bb = fc.map(FileChannel.MapMode.READ_ONLY, 0, sz);

    // Decode the file into a char buffer
    CharBuffer cb = decoder.decode(bb);

    // Perform the search
    grep(f, cb);

    // Close the channel and the stream
    fc.close();
  }

  public static void main(String[] args) {
    if (args.length < 2) {
      System.err.println("Usage: java Grep pattern file...");
      return;
    }
    compile(args[0]);
    for (int i = 1; i < args.length; i++) {
      File f = new File(args[i]);
      try {
        grep(f);
      } catch (IOException x) {
        System.err.println(f + ": " + x);
      }
    }
  }

}

           
       

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