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How to access Java property in terminal

I know I can get all the Java System properties from the terminal using
java -XshowSettings:properties -version
How do I access just one specific java system property?
For example, like "user.name"?
I want to do this in the terminal, not with Java.

Solution as a one liner script. Just change the val variable to the key you want to print:
val='java.library.path'; java -XshowSettings:properties -version 2>&1 | sed -re 's/^ +[^=]+ =/_&/' | gawk -v key=$val 'BEGIN{ RS="_"; IFS=" = "} { if($1 ~ key){ print $0 }}'
Details
Some property values like java.library.path contain new lines so we need to mark records before filtering and printing them.
sed allows us to do that, then awk can be used to filter and print.
java -XshowSettings:properties -version 2>&1 |\
sed -re 's/^ +[^=]+ =/_&/' |\
gawk -v key=java.library.path 'BEGIN{ RS="_"; IFS=" = "} { if($1 ~ key){ print $0 }}'
Result:
java.library.path = /usr/java/packages/lib/amd64
/usr/lib64
/lib64
/lib
/usr/lib
Pipeline parts explained:
2>&1: properties are printed to stderr so we need to redirect them to stdin.
sed -re 's/^ +[^=]+ =/_&/' : add an underscore in front of interesting lines, those starting with 4 spaces and containing =.
gawk -v key=java.library.path: set keyawk variable to the selected property key.
'BEGIN{ RS="_"; IFS=" = "}: set record separator to '_' and input field separator IFS to =.

If you need the current logged in user in bash just use whoami command. If you want to get the java property from terminal you can use the following command
java -XshowSettings:properties -version 2>&1 | grep user.name
which will print
$java -XshowSettings:properties -version 2>&1 | grep user.name
user.name = user
If you just need the user name only
java -XshowSettings:properties -version 2>&1 | grep user.name | cut -c 16-100
which will print
$java -XshowSettings:properties -version 2>&1 | grep user.name | cut -c 16-100
user

You can't.
What you can do is create a java file to get the information and run with java, here the documentation.
Since you already said that you don't want this, you can grep (filter) the output of
java -XshowSettings:properties -version 2>&1 | grep java.home
java.home = /usr/java/jdk1.8.0_112/jre
If you want to know the system properties of a running jvm, use the jcmd tool
jcmd PID VM.system_properties

How to distinguish running java programs

Our server machine runs many java programes. And some of them are launched with the command "java -jar ***.jar". but sometimes I have to stop one to update the class files in it. the problem is how can i fingure out which program is the one i want to stop, or is there a tool I can use to find out the executable jar files' location.

You can use jps command.
$ jps -v
34370 Jps -Dapplication.home=/Library/Java/JavaVirtualMachines/jdk1.8.0_20.jdk/Contents/Home -Xms8m
34341 main -XX:+TieredCompilation -Xbootclasspath/a:/usr/local/Cellar/leiningen/2.5.0/libexec/leiningen-2.5.0-standalone.jar -Dfile.encoding=UTF-8 -Dmaven.wagon.http.ssl.easy=false -Dleiningen.original.pwd=/Users/ntalbs/js-workspace/synapeditor_mobile -Dleiningen.script=/usr/local/bin/lein
jps will display all java processes. The first column is OS pid. You can check the messages on console, then kill what you want. Perhaps you want to check jps document from Oracle.
Also, you can use ps and grep command.
$ ps -ef | grep java
or
$ ps -aux | grep java

How to create a script to restart a JAR file and get output in a terminal?

I have used the following scripting for start and stop a jar file.
**start.sh**
#!/bin/bash
nohup nice java -jar Server.jar > ./Server.out 2>&1 &
**stop.sh**
#!/bin/bash
kill `ps -ef | grep Server.jar | grep -v grep | awk '{ print $2 }'`
Now I want to merge both scripts and create a new restart script. I also want this script output in a terminal instead of a text file(Server.out).
Would appreciate any kind of input/help.

You can either put the commands of the two sripts after each other (kill first, java second) or just call the two scipts in the appropriate order.
The idea is that restart is basically equivalent to killing the current running version and starting a new one.
To avoid the output to a file, remove the > ./Server.out part.
Edit: removed note about removing the redirection part as I misread the grep part of the kill script
Update: Missed the nohup part of the script: with nohup you need to redirect output to a file, because the process is detached from the terminal (see documentation). If you do want to see the output in the terminal, remove nohup as well as the redirection to the file

linux shell script in java

I am using below shell code in linux i want it to make it in Java.I want to call this command in JAVA
mailq | grep -B1 -i temporarily | grep -iv deferred | \
egrep -i 'jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec' | \
awk -F" " '{print $1}' | awk '{print substr($0,10,14)}'
mailq command shows the queued mail messages with there respective Id and there errors .
Like in command above i am looking for messages with temporarily disabled message in it and taking the above message where its id is present in **09089 like this checking the month and than printing the last 5 characters of that id

String cmd = "mailq | grep -B1 -i temporarily | grep -iv deferred | "
+"egrep -i 'jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec' |"
+ " \'{print $1}\' | awk \'{print substr($0,10,14)}\'";
try
{
ProcessBuilder pb = new ProcessBuilder("bash", "-c", cmd);
Process p = pb.start();
p.destroy();
}
catch (Exception e)
{e.printStackTrace();}

here
http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html

In general this type of issues is handled in java by 'Runtime' class.
Here Runtime example java
you can find an example of how to do that
The newer approach would be using ProcessBuilder class though

If I understood correctly, you want to do the same thing that this shell command, but in pure Java, not by running it from Java. One advantage of the port can be portability.
I think you want JavaMail to do the mail access. I am not a specialist of this API, but I used it in a small Processing program to show its usage: Email sketch.
Then you need to filter out the results and to isolate the part you want, which isn't very hard.

Running Different Bash Commands Based on Java Version

I'm trying to develop a bash build script for a Java project that will be run on Ubuntu and Fedora. Ubuntu uses the gcj compiler while Fedora uses IcedTea.
Both report their errors and warning in slightly different ways, and I want to ignore the warnings (I know, not generally a good idea, but some of the warnings are simply idiotic).
For gcj, I want to run:
javac *.java 2>&1 | grep -A 4 "error:"
but for IcedTea, I want to run:
javac *.java 2>&1 | grep -A 4 "error:\|errors\|.java:"
I'm still new to bash, so how would I write an if statement that would run one versus the other based upon the javac version?

Assuming your java and javac binaries match, and that icedtea is the special case.
#!/bin/bash
ERROR="error:"
java -version 2>&1 | grep -i icedtea > /dev/null
if [ $? -eq 0 ]; then
ERROR="error:\|errors\|.java:"
fi
javac *.java 2>&1 | grep -A 4 $ERROR
On my system, icedtea and sun have the same output for "javac -version", but not for "java -version".

Writing Java build scripts in bash (or any other shell language) has a number of problems:
scripts tend to be non-portable due to shell differences, different command locations, incompatible command options and so on ... even if you try to make the portable.
scripts cannot cope with dependencies (or at least not easily)
scripts cannot cope with recompiling only stuff that has changed
Instead, I suggest that you write a "build.xml" file and use the Ant build tool. Ant has the advantage of running on any build platform that runs Java, and of taking care of the vast majority of platform differences. It is sort of like a better "Make" designed specifically for building Java.

#!/bin/sh
JAVAC_VERSION="`java -version 2>&1 /dev/null | awk '/IcedTea/ {print $4}' | sed -e 's/[\(0-9]//g'`"
ICEDTEA="IcedTea"
if [ ${JAVAC_VERSION} = ${ICEDTEA} ]; then
javac *.java 2>&1 | grep -A 4 "error:\|errors\|.java:"
else
javac *.java 2>&1 | grep -A 4 "error:"
fi
exit 0
That should do it - if i understood your question correctly. How you get the version - im not quite sure of, but if my javac -version is incorrect just change it accordingly to your needs.