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Environment variables

An environment variable is a dynamic value loaded into the memory that can be used by several processes operating simultaneously. On most operating systems, the location of some libraries or of the main system executables may be different depending on the installation.

It is therefore possible, from a given programme, to refer to a location based on the environment variables that define these data.

In Windows

In Windows, the environment variables are placed between the "%" character. Thus to display the value of an environment variable, simply type following type of command:

echo %NAME_OF_THE_VARIABLE%

Here is a non-exhaustive list of the main environment variables on Windows systems:

In Windows, the set command allows creation, modification and display of the environment variables. However, changes are made only in the session in progress.

To display a variable, the following command is used:

set VariableName 

To create a variable, the following command is used:

set VariableName=value

To delete a variable, the following command is used:

set VariableName=

set colour=black^&white
	or
set varname="new&name"

In UNIX

In UNIX systems, the environment variables are preceded by the "$" character and placed between braces, even though the braces are not compulsory. Given the variety in UNIX systems (particularly the different Linux distributions), the environment variables Thus to display the value of an environment variable, simply type one of the following commands:

echo $VARIABLE
echo ${VARIABLE}

Here is a non-exhaustive list of the main environment variables on UNIX systems: