Display or print UNIX / Linux path ~ $PATH variable

In UNIX / Linux file systems, the human-readable address of a resource is defined by PATH. On Unix / Linux like operating systems, (as well as on DOS / Windows and its descendants), PATH is an environment variable listing a set of paths to directories where executables may be found.
Display current PATH

Use echo command:
$ echo $PATH
Output:

/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/bin/X11:/usr/games

Modify current PATH

Use export command to add /opt/games to PATH, enter:
export PATH=$PATH:/opt/games

To format your PATH variable for easy viewing, add following code to your bash startup file (such as ~/.bashrc or ~/.bash_profile) :

function path(){
old=$IFS
IFS=:
printf "%s\n" $PATH
IFS=$old
}

(Function credit: usenet archive)

Now just run path:
$ path
Output:

/usr/local/sbin
/usr/local/bin
/usr/sbin
/usr/bin
/sbin
/bin
/usr/bin/X11
/usr/games

Source: http://www.cyberciti.biz/faq/howto-print-path-variable/

How to Find the JAVA HOME Directory in ubuntu linux

Code:

$ whereis java
java: /usr/bin/java /etc/java /usr/share/java

That tells the command java resides in /usr/bin/java.

Dig again:

Code:

$ ls -l /usr/bin/java
lrwxrwxrwx 1 root root 22 2009-01-15 18:34 /usr/bin/java -> /etc/alternatives/java

So, now we know that /usr/bin/java is actually a symbolic link to /etc/alternatives/java.

Dig deeper using the same method above:
Code:

$ ls -l /etc/alternatives/java
lrwxrwxrwx 1 root root 31 2009-01-15 18:34 /etc/alternatives/java -> /usr/local/jre1.6.0_07/bin/java

So, thats the actual location of java: /usr/local/jre.....
You could still dig deeper to find other symbolic links.

Source: http://ubuntuforums.org/showthread.php?t=1054731

How to set JAVA HOME path in Linux

~/.bash_profile is a startup script which generally runs once. This particular file is used for commands which run when the normal user logs in. Common uses for .bash_profile are to set environment variables such as PATH, JAVA_HOME, to create aliases for shell commands, and to set the default permissions for newly created files.
Set JAVA_HOME / PATH for single user

Login to your account and open .bash_profile file
$ vi ~/.bash_profile
Set JAVA_HOME as follows using syntax export JAVA_HOME=. If your path is set to /usr/java/jdk1.5.0_07/bin/java, set it as follows:
export JAVA_HOME=/usr/java/jdk1.5.0_07/bin/java
Set PATH as follows:
export PATH=$PATH:/usr/java/jdk1.5.0_07/bin
Save and close the file. Just logout and login back to see new changes:
$ echo $JAVA_HOME
$ echo $PATH
Tip: Use the following command to find out exact path to which java executable under UNIX / Linux:
$ which java

Please note that the file ~/.bashrc is similar, with the exception that ~/.bash_profile runs only for Bash login shells and .bashrc runs for every new Bash shell.
Set JAVA_HOME / PATH for all user

You need to setup global config in /etc/profile OR /etc/bash.bashrc file for all users:
# vi /etc/profile
Next setup PATH / JAVA_PATH variables as follows:
export PATH=$PATH:/usr/java/jdk1.5.0_07/bin
export PATH=$PATH:/usr/java/jdk1.5.0_07/bin


Source: http://www.cyberciti.biz/faq/linux-unix-set-java_home-path-variable/