Every once in awhile, I need to backup a large directory from another computer. This can be done by creating a zip or tar of the files you are looking to save and then copying those zips to the other computer. But what it you have a very large directory and not enough room to store the extra file. Here is a way to use tar over ssh:

ssh tar zcvf – /wwwdata | ssh root@backupserver.mydomain.com “cat > /backup/wwwdata.tar.gz”

Did you know? You can Set file timestamp using touch command. One way to do this is:
touch -c -t YYMMDDhhmm filename.txt

The other day I had to write a script to change to a working directory and back to the original directory. The problem was they were on different drives on Windows. So I had to find a way to capture the drive letter
and switch back to that drive. When using the following command,

cd F:somedir

you are not moved to the “F:” drive without an explicit “F:” command.

The cd Command on windows will show the current directory location. Using some string manipulation on that and capturing it to a variable allows us to go back to that drive.

REM Capture the current drive letter
set ORIGDRIVE=%cd:~0,2%

F:
REM some other scripting things here

REM Return to the original drive letter
ORIGDRIVE

The first line captures the current drive letter by specifying the first character with 0 and the ,2 states to pick up the next 2 characters which would hold the “C:” or whatever drive you started on.

Tags: BAT, DOS, scripting, Windows

I had to write a backup script the other day and used the find command to find the files that were older than a given amount of days.

DAYS_TO_KEEP=7
find /path/to/files* -type f -name *.bak -mtime $DAYS_TO_KEEP -exec rm {} ;

The -name argument uses the escaped asterisk so command completion does not replace it with all the file names.

The -mtime argument takes a number that is the number of days to look at.

The -exec argument takes a command and the {} is replaced with the current file name and the ; is the end of the command.

This is a small part of the power of the find command.

So every once in a while I want to see the progress of an upload or backup. So I turn to the watch command in Linux. The watch command gives the user the ability to re-run a command and see the updated output.

The syntax is ‘watch -n -d .

So for watching a file downloads progress you could run the following:

watch -n 30 ls -l filedownloading

This would show the ls output and you could watch the size of the file grow as it is dowload progress.

When attempting to run ant I get the following message: “Unable to locate tools.jar. Expected to find it in C:Program Files (x86)Javajre6libtools.jar”

This had to do with my JAVA_HOME not pointing to a Java JDK.

So if you download a JDK and update your JAVA_HOME environment variable to point to that directory, ant should run happily.

In BASH:
export JAVA_HOME=/path/to/jdk

IN DOS:
set JAVA_HOME=c:PATHtojdk

Tags: ant, Java

Every once in awhile I go back and try to figure out how to create a basic ant build.xml file. So I am just placing a sample build.xml here.

The directory structure should be something like
./build.xml
./src/HelloWorld.java

The targets will create the build directory and compile the source and run a test execution of the class.

<project name="HelloWorld" basedir="." default="main">
<target name="clean">
<delete dir="build"/>
</target>

<target name="compile">
<mkdir dir="build/classes"/>
<javac srcdir="src" destdir="build/classes"/>
</target>

<target name="jar" depends="compile">
<mkdir dir="build/jar"/>
<jar destfile="build/jar/HelloWorld.jar" basedir="build/classes">
<manifest>
<attribute name="Main-Class" value="HelloWorld"/>
</manifest>
</jar>
</target>

<target name="run" depends="jar">
<java jar="build/jar/HelloWorld.jar" fork="true" />
</target>

<target name="main" depends="clean,run"/>

</project>

Tags: ant

I had recently reinstalled my system and was trying to run a simple class that consisted
of a “Hello World” program in Java. I received the following:

Compile:

$> javac LottoMain.java

Run:

$> java LottoMain

Exception in thread “main” java.lang.NoClassDefFoundError: LottoMain
Caused by: java.lang.ClassNotFoundException: LottoMain
at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:319)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:264)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:332)
Could not find the main class: LottoMain. Program will exit.

The compile line completed without errrors and the LottoMain.class file was there, but
what I didn’t know was that I no longer had the current directory “.” in my CLASSPATH variable.

After adding “.” to my CLASSPATH variable the run command gave me what I was expecting.

Run:

$> java LottoMain

Hello Eric!

Updating the CLASSPATH variable in Bash:
in my home directory/.bashrc file

export CLASSPATH=$CLASSPATH:.

Tags: Java, Programming

Starting on my road to creating a Java based GUI I stumbled upon the following link within the “Creating a GUI with JFC/Swing” Train in the Java Tutorials from Oracle.

Using Swing Components: Examples

It has code examples and can really get you started on the road to a Java GUI interface.

Tags: GUI, Java, Swing

This is the First of some basic articles about creating a GUI in Java. The following code is the basis of the following series of articles. I am using the Java Swing window toolkit.

import java.awt.*;
import java.swing.*;

class FirstWindow 
{

  public static void main(String[] args)
  {
      //Create Window object and set title bar text
      JFrame frame = new frame("First Window");

      // Set the Default operation when you close the window
      // This exits the program on closing the window
      // The default behavior is to HIDE_ON_CLOSE
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

      // Now we need to Display the window
      // The null argument will place the element in the center of the screen.
      frame.setLocationRelativeTo(null);
      frame.pack();
      frame.setVisible(true);
   }
}

This is enough to display a simple window, but it will probably not have any useful size associated with it and it does not do anything.

The next step will be to add some useful widgets and eventually functionality to make the window useful.

Helpful info:
Java: Great link to Swing Examples

Tags: Java, Swing