Environment Variables

Here are my notes on setting up Environment Variables on Microsoft Windows and (in the future) other operating systems.

War drums is my theme music for this topic.

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What Are Environment Variables?

Environment Variables are stored in a small area of memory available to all programs running within or on top of the DOS environment (including Windows). They are called “variables” because they can be changed. In fact, some variables need to be reestablished after every reboot.

• Variable names are NOT case sensitive within Windows.

For the Ruby language, Facter stores and retrieves "facts" from operating systems.

Related:

Windows System Environment Variables

These system environment variables are automatically created by Windows upon boot-up in Windows Registry key HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Control\ Session Manager\ Environment

Variable	Sample Typical Value
%SystemDrive%	C:
%SystemRoot%	C:\WINDOWS C:\WINNT
%WinDir%	C:\WINDOWS C:\WINNT
%SystemDirectory%	C:\WINDOWS\System32 C:\WINNT\System32
%ComSpec%	C:\WINDOWS\system32\cmd.exe The path including the command interpreter program.
%programfiles%	C:\WINDOWS\Program Files
%Temp%	C:\Users\W\AppData\Local\Temp on Windows Vista & 2008 C:\DOCUME~1\Usr\LOCALS~1\Temp (compressed form of) C:\Documents and Settings\Usr\Local Settings\Temp
%Tmp%
%HOMEDRIVE%	C: The drive letter associated with the user's home directory
%HOMEPATH%	The path to the user's home directory as defined in UMD/AD (excluding drive): \Users\<USERNAME> on Windows Vista & 2008 \Documents and Settings\Guest on Windows XP
%OS%	Windows_NT (even on Windows Vista & XP machines The operating system the user is running
%USERDOMAIN%	The name of the domain that contains the user's account. On a stand-alone machine, the same as the machine name.
%USERNAME%	The user's name
%USERPROFILE%	C:\Users\<USERNAME> — The user's root folder
%USERPROFILE%\Desktop	The user's desktop folder

If you have the permissions, invoke, then open my DOS batch file 1envvars.bat which lists the values of these variables on your computer

Windows resolves commands typed in the start/run box first from files in %SYSTEMDRIVE%, then files in %SYSTEMROOT%. This is regardless of the systemdrive (such as E:) being later in the path. This means that a rogue file can be invoked instead of a good file (such as cmd.exe) if it's in the %SYSTEMDRIVE%.

Below are dynamic environment variables:

User Environment Variables Added by Applications

User environment variables are stored in Windows Registry HKEY_CURRENT_USER\Environment

Within a command batch file, to list Oracle Environment Variables

echo ORACLE_SID = %ORACLE_SID%
echo ORACLE_HOME = %ORACLE_HOME%
echo ORA_NLS = %ORA_NLS%

echo.
echo PATH = %PATH%

echo.
echo Machine Name to messenger service:
net name

Novell adds these environment variables during installation.

Variable
%USER%
%NWUSERNAME%
%NWLANGUAGE%

Creating Variables on Windows

Environment Variables can be created and changed using several mechanisms:
1. By Windows automatically upon boot-up.

2. By application programs using Windows OS API functions. This is commonly done by application installation programs.

3. Manually using GUI in System Properties, Advanced tab, Environment Variable button. Get to this one of two ways:
   a). right-click My Computer icon, select Properties,
   b). click Start > Control Panel > System icon

   Click the Advanced tab, New for a new variable or Edit for an existing variable listed.

   

   System variables are available to all users.

4. Manually using commands typed into the DOS Command Window obtained one of two ways:
   a). click Programs | Accessories | Command Prompt
   b). click Run..., type cmd and press Enter.

   To see all variables, type:

   SET

   Windows uses a tilde ~ character to substitute for parts of file and folder names longer than 8 characters.

   To use the SET command to define a single variable:

   SET CLASSPATH=.;path1

   The dot specifies the current directory. The semicolon separates two folders. If the variable was already established, this will replace its value.

   To add a value in front of the existing value, refer to itself:

   SET CLASSPATH=path1;%CLASSPATH%

   Variables created with SET are only valid for the current session and will not be available after the command window is closed or the computer reboots.

5. By commands executed from within an AUTOEXEC.BAT file or host script file

   run this sample logon.bat file. (Click Open when prompted. Your firewall may -- rightfully -- block this.)
   

MS PATH

The operating system looks for executables down the list of folders listed in the PATH User variable. The operating system uses the first occurance it finds. So watch out for multiple versions of the same program. For example, the Oracle install automatically adds:

Program Files\Oracle\JRE\1.1.7\Bin;

To enable command line invocation of compiler program csc.exe of the Microsoft .NET Framework, add this to the end of your PATH environment variable.

1. Click
2. Right-click on "My Computer" to select Properties.
3. Click the "Advanced" tab.
4. Click the "Environment Variable" button.
5. Scroll down the "System variables" list to the "Path" variable.
6. Double click on "Path"
7. Press the "End" key
8. Type (beginning with a semicolon separator) ;%systemroot%Microsoft.NET\Framework\v1.1.4322
9. Click "OK"
10. Click "OK" to close the System Properties window.

Verify the change:

1. Click
2. Click Run... for a Run window.
3. Type "cmd" in the Open: field.
4. Click "OK"
5. Type a command such as "csc"
6. You are unsuccessful if you get back a response such as

   'csc' is not recognized as an internal or external command,
   operable program or batch file.

To spare its users, most commercial applications provide an installer which does this automatically. For example, Microsoft .NET Framework SDK has a vcvars32.bat file to update paths on Windows 9x machines.

Avoid spaces in path names (for backward compatibility and to avoid trouble) by using the 8 character equivalents.
For example, to reach

C:\Program Files\Mercury Interactive\Mercury LoadRunner\bin
specify
C:\PROGRA~1\MERCUR~1\MERCUR~1\bin

The sequence in my PATH:

1. C:\PROGRA~1\Java\jdk1.5.0_02\bin;
2. C:\PROGRA~1\MERCUR~1\MERCUR~1\classes;
3. %SystemRoot%\system32;
4. %SystemRoot%;
5. %SystemRoot%\System32\Wbem;
6. %systemroot%\Microsoft.NET\Framework\v1.1.4322;
7. C:\Program Files\Microsoft SQL Server\80\Tools\Binn\;
8. c:\Program Files\Microsoft Visual Studio .NET 2003\SDK\v1.1\Bin;
9. c:\program files\microsoft platform sdk for windows xp sp2\include

UNIX Environment Variables

In UNIX/Linux systems, to list environment variables:
env

In UNIX/Linux systems, add a dollar sign ($) in front of each variable name in all caps:

echo $LOGNAME	user name used for login
echo $USER	user name (sudo)
echo $UID	user name	Solaris
echo $SHELL	directory containing OS shell executables
echo $PATH	directories containing executables, searched to find applications when no absolute path is specified on the command line.
echo $LD_LIBRARY_PATH	path to system and user libraries
echo $MANPATH	directory containing manuals
echo $HOME	directory of user's home directory
echo $TZ	time zone, such as "US/Mountain"

In UNIX systems, the colon (:). In Windows systems, the semi-colon (;) is used. So to list each path in a separate line:

echo $PATH | tr ':' '\n'

Solaris systems have additional ones, including:

echo $BASH	path to the shell on the file system.
echo $HOSTNAME	name of the current system.
echo $PPID	parent process ID
echo $WINDOWMANAGER	name of the X11 window manager
echo $COLUMNS	The column width for the terminal
echo $DISPLAY	The display variable used for X11 graphics.

Creating Variables on Linux

To update an environment variable that lives until the next reboot:
#export PATH=”/usr/local/XXX/bin:$PATH”
#echo $PATH

Notice that colons are used to separate path items.

To create an environment variable that lives forever, update your .bash_profile file:

XXXPATH=”/usr/local/XXX/bin”
export XXXPATH

For a list of environment settings (arguments) for a process with PID 23141 (on Solaris):

pargs -ae 23141

Java Environment Variables

JDK versions 1.2 and 1.3 require variables Xrunmic_supp and Xbootclasspath %mic_class%

The Java interpreter searches the PATH for a class by name and loads the first one it finds. So specify your own library and the most recent library first (especially if you use the same name as a class in a standard library).

Also, for best performance, place the most-often used libraries at the front of the path. This applies to LIBPATH and LD_LIBRARY_PATH variables for most often used JNI libraries.

Java 1.4 Documentation on Classpath notes that the preferred method for command-line tools such as java, javac, or javadoc is to NOT use environment variables but instead specify -classpath as part of the command invoking a Java program.

The System environment variable CLASSPATH must be in upper case (not “classpath”). CLASSPATH is used to specify the full path and file name of every jar file used by java programs. Thus CLASSPATH could be quite long.


C:\jdk1.3.1_01\src.jar;
C:\jdk1.3.1_01\lib\dt.jar;
C:\jdk1.3.1_01\lib\tools.jar;
C:\jdk1.3.1_01\jre\lib\il8n.jar;
C:\jdk1.3.1_01\jre\lib\jaws.jar;
C:\jdk1.3.1_01\jre\lib\rt.jar;
C:\jdk1.3.1_01\jre\demo\sound\JavaSound.jar;
C:\jdk1.3.1_01\demo\jfc\SwingSet2\SwingSet2.jar;
C:\jdk1.3.1_01\demo\jfc\SwingApplet\SwingApplet.jar;

Sun's JDK adds:

C:\jdk1.3.1_01\;
C:\jdk1.3.1_01\Bin;
C:\jdk1.3.1_01\Lib;

A common mistake with CLASSPATH is to specify only folder paths and leave out jar file names. Semicolons should separate each jar file specification.

On client machines, Microsoft's VM CLASSPATH is, by default:

%windows%\Java\Classes\Classes.zip;

This string is stored in environment variable CLASSPATH or Windows registry key

HKLM\Software\Microsoft\Java VM\Classpath

Windows 95/98 computers should limit CLASSPATH to less than 400 characters.

Dick Baldwin notes in his tutorial that if you want the CLASSPATH to point to class files that belong to a package, you should specify a path name that includes the path to the directory one level above the directory having the name of your package.

For example, suppose you want the Java interpreter to be able to find classes in the package mypackage. If the path to the mypackage directory is C:\java\MyClasses\mypackage, you would set the CLASSPATH variable as follows:

set CLASSPATH=C:\java\MyClasses

The purpose of the package directive is to identify a particular class (or group of classes contained in a single source file (compilation unit)) as belonging to a specific package.

NOTE: Training connection also offers some great tutorials on Java programs, Dreamweaver training, and Flex software.

In Linux: pCLASSPATH=/usr/local/java/jre/bin

My CLASSPATH:

1. C:\PROGRA~1\MERCUR~1\MERCUR~1\classes;
2. C:\PROGRA~1\MERCUR~1\MERCUR~1\classes\srv;
3. C:\PROGRA~1\Java\jdk1.5.0_02\lib\rt.jar

Amazon EC2 File Paths

Amazon EC2 command script users add these environment variables. For example, if EC2 files are located in folder C:\EC2:

Variable	Sample
EC2_HOME	C:\EC2 where files are located
EC2_PRIVATE_KEY	C:\EC2\pk.pem full path to file
EC2_CERT	C:\EC2\509cert.pem full path to file

Windows Network Shares

Changes to variables disappear after reboot.
So change the variables in a shell script or Windows network share. This mapdir.bat is an example of allocating the X: drive.

...

This assumes that the loopback IP address has not been changed in the hosts file.

Microsft T-SQL to Read Windows environment variables

To read Windows environment variables using Microsoft SQL Server T-SQL code:

-- Display all environment variables
EXEC master..xp_cmdshell 'set'
------------
 
-- Retrieve a single environment variable - Read environment variable
DECLARE @EnvVar nvarchar(256)
CREATE TABLE #Upload(EnvVar nvarchar(256))
INSERT INTO #Upload
EXEC xp_cmdshell 'echo %USERDOMAIN%'
DELETE #Upload WHERE EnvVar is NULL OR EnvVar = ''
SET @EnvVar = (SELECT EnvVar from #Upload)
SELECT @EnvVar as [User Domain]
/* User Domain ENTERPRISE */
DROP TABLE #Upload

Source: sqlusa.com