/**
* 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" +
"-f: 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;
}
}