| /** |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package org.apache.hadoop.fs.shell; |
| |
| import java.io.IOException; |
| import java.util.LinkedList; |
| import java.util.List; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| import org.apache.hadoop.fs.FSDataInputStream; |
| import org.apache.hadoop.fs.PathIsDirectoryException; |
| import org.apache.hadoop.io.IOUtils; |
| |
| /** |
| * Get a listing of all files in that match the file patterns. |
| */ |
| @InterfaceAudience.Private |
| @InterfaceStability.Unstable |
| |
| class Tail extends FsCommand { |
| public static void registerCommands(CommandFactory factory) { |
| factory.addClass(Tail.class, "-tail"); |
| } |
| |
| public static final String NAME = "tail"; |
| public static final String USAGE = "[-f] <file>"; |
| public static final String DESCRIPTION = |
| "Show the last 1KB of the file.\n" + |
| "\t\tThe -f option shows appended data as the file grows.\n"; |
| |
| private long startingOffset = -1024; |
| private boolean follow = false; |
| private long followDelay = 5000; // milliseconds |
| |
| @Override |
| protected void processOptions(LinkedList<String> args) throws IOException { |
| CommandFormat cf = new CommandFormat(1, 1, "f"); |
| cf.parse(args); |
| follow = cf.getOpt("f"); |
| } |
| |
| // TODO: HADOOP-7234 will add glob support; for now, be backwards compat |
| @Override |
| protected List<PathData> expandArgument(String arg) throws IOException { |
| List<PathData> items = new LinkedList<PathData>(); |
| items.add(new PathData(arg, getConf())); |
| return items; |
| } |
| |
| @Override |
| protected void processPath(PathData item) throws IOException { |
| if (item.stat.isDirectory()) { |
| throw new PathIsDirectoryException(item.toString()); |
| } |
| |
| long offset = dumpFromOffset(item, startingOffset); |
| while (follow) { |
| try { |
| Thread.sleep(followDelay); |
| } catch (InterruptedException e) { |
| break; |
| } |
| offset = dumpFromOffset(item, offset); |
| } |
| } |
| |
| private long dumpFromOffset(PathData item, long offset) throws IOException { |
| long fileSize = item.refreshStatus().getLen(); |
| if (offset > fileSize) return fileSize; |
| // treat a negative offset as relative to end of the file, floor of 0 |
| if (offset < 0) { |
| offset = Math.max(fileSize + offset, 0); |
| } |
| |
| FSDataInputStream in = item.fs.open(item.path); |
| try { |
| in.seek(offset); |
| // use conf so the system configured io block size is used |
| IOUtils.copyBytes(in, System.out, getConf(), false); |
| offset = in.getPos(); |
| } finally { |
| in.close(); |
| } |
| return offset; |
| } |
| } |