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Bash Script

Posted on 2013-02-04
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Last Modified: 2013-02-04
Can someone help me understanding  what the this script is doing?
I found this script on the internet. I would like to create my own script to run my own java programs automatically. I'm new to the linux environment. I appreciate your help.

#!/bin/bash
JAVA_HOME=/usr/lib/jvm/jdk1.6.0_02
CLASSPATH=/home/freddy/myapp/lib/whatever.jar: .
$JAVA_HOME/bin/java -cp $CLASSPATH MyJavaClass
exit 0

Things I do know. I know how to open the terminal and start the vi editor. I have a cheat sheet to help with this. I have added my script directory to the PATH, so my scripts run by using the relative path.

Things I don't know: How to create a jar in eclipse?(Looking it up now.) Where is JAVA_HOME and CLASSPATH.

I'm a newbie and appreciate your help.
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Question by:DOCDGA
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Expert Comment

by:omarfarid
ID: 38852533
to know the locations you can run below commands from command prompt

echo $JAVA_HOME

echo $CLASSPATH.
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Author Comment

by:DOCDGA
ID: 38852604
I tried running the commands : echo $JAVA_HOME echo $CLASSPATH and the results came back blank
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omarfarid earned 250 total points
ID: 38852611
Ok, they are not set before and are set in the script
:

JAVA_HOME is /usr/lib/jvm/jdk1.6.0_02

and

CLASSPATH is /home/freddy/myapp/lib/whatever.jar: .
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Expert Comment

by:tel2
ID: 38852707
Hi DOCDGA,

> Can someone help me understanding  what the this script is doing?
I'll give a brief explanation of each line, below.

#!/bin/bash
Run this script as a bash script (i.e. in the borne again shell, which I think is the most common one these days).

JAVA_HOME=/usr/lib/jvm/jdk1.6.0_02
Assign a single path to an environment variable

CLASSPATH=/home/freddy/myapp/lib/whatever.jar: .
Assign 2 paths to an environment variable, the 2nd being "." which means "the current working directory".  The ":" separates the paths, but I doubt the space before the last "." needs to be there.

$JAVA_HOME/bin/java -cp $CLASSPATH MyJavaClass
Run java from /usr/lib/jvm/jdk1.6.0_02/bin/java with switch(es) "-cp" (whatever that means), and arguments "/home/freddy/myapp/lib/whatever.jar: ." and "MyJavaClass".

exit 0
Exit the script, forcing a zero return code, which usually means "success".  Usually having an exit at the end of a script is unnecessary, except if you want to force a particular return code, as in this case.  This means that even if the previous line fails with a non-zero return code, the script will still return a zero return code.
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Author Comment

by:DOCDGA
ID: 38852717
Okay, I'm a little lost. Please forgive me for not understanding but I am new to  programming. I did manage to navigate to through the directories and
locate/usr/lib/jvm
I don't see any jdk file but I see a bunch of directories with names like java-1.5.0-gcj-1.5.0., jre,jre-1.5.0,java-17.0-openjdk-1.7.0.9, jre-1.7.0-openjdk,jre-gcj, and jre-openjdk

Don't know if this makes much since but I'm just trying to learn.
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Expert Comment

by:tel2
ID: 38852723
What output do you get when you issue this command, DOCDGA?
    ls -l /usr/lib/jvm/jdk1.6.0_02/bin/java
Please copy and paste the above command, to avoid typos.
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Author Comment

by:DOCDGA
ID: 38852801
ls: cannot access /usr/lib/jvm/jdk1.6.0_02/bin/java: No such file or directory
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Assisted Solution

by:tel2
tel2 earned 250 total points
ID: 38852825
Which confirms that that path doesn't exist on your machine.  I don't know the java environment, so someone else will have to help with that issue, sorry.
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