/*
* The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
* (the "License"). You may not use this work except in compliance with the License, which is
* available at www.apache.org/licenses/LICENSE-2.0
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
* either express or implied, as more fully set forth in the License.
*
* See the NOTICE file distributed with this work for information regarding copyright ownership.
*/
package alluxio.shell.command;
import alluxio.AlluxioURI;
import alluxio.Constants;
import alluxio.client.ReadType;
import alluxio.client.file.FileInStream;
import alluxio.client.file.FileSystem;
import alluxio.client.file.URIStatus;
import alluxio.client.file.options.OpenFileOptions;
import alluxio.exception.AlluxioException;
import alluxio.exception.ExceptionMessage;
import com.google.common.base.Preconditions;
import org.apache.commons.cli.CommandLine;
import org.apache.commons.cli.Option;
import org.apache.commons.cli.Options;
import java.io.IOException;
import javax.annotation.concurrent.ThreadSafe;
/**
* Prints the file's last n bytes (by default, 1KB) to the console.
*/
@ThreadSafe
public final class TailCommand extends WithWildCardPathCommand {
/**
* @param fs the filesystem of Alluxio
*/
public TailCommand(FileSystem fs) {
super(fs);
}
@Override
public String getCommandName() {
return "tail";
}
@Override
protected void runCommand(AlluxioURI path, CommandLine cl) throws AlluxioException, IOException {
URIStatus status = mFileSystem.getStatus(path);
int numOfBytes = Constants.KB;
if (cl.hasOption('c')) {
numOfBytes = Integer.parseInt(cl.getOptionValue('c'));
Preconditions.checkArgument(numOfBytes > 0, "specified bytes must be > 0");
}
if (status.isFolder()) {
throw new IOException(ExceptionMessage.PATH_MUST_BE_FILE.getMessage(path));
}
OpenFileOptions options = OpenFileOptions.defaults().setReadType(ReadType.NO_CACHE);
try (FileInStream is = mFileSystem.openFile(path, options)) {
byte[] buf = new byte[numOfBytes];
long bytesToRead;
if (status.getLength() > numOfBytes) {
bytesToRead = numOfBytes;
} else {
bytesToRead = status.getLength();
}
is.skip(status.getLength() - bytesToRead);
int read = is.read(buf);
if (read != -1) {
System.out.write(buf, 0, read);
}
}
}
@Override
public String getUsage() {
return "tail -c <number of bytes> <path>";
}
@Override
public String getDescription() {
return "Prints the file's last n bytes (by default, 1KB) to the console.";
}
@Override
public Options getOptions() {
Option bytesOption =
Option.builder("c").required(false).numberOfArgs(1).desc("user specified option").build();
return new Options().addOption(bytesOption);
}
}