Writes an environment variable.
EnvSet ( "envvariable" [, "value"] )
| envvariable | Name of the environment variable to set. | 
| value | [optional] Value to set the environment variable to. If a value is not used the environment variable will be deleted. | 
| Success: | not 0. | 
| Failure: | 0. | 
A environment variable set in this way will only be accessible to programs that AutoIt spawns (Run(), RunWait()). Once AutoIt closes, the variables will cease to exist.
#include <MsgBoxConstants.au3>
Example()
Func Example()
    ; Create an environment variable called %MYVAR% and assign it a value. When you assign or retrieve an environment variable you do so minus the percentage signs (%).
    EnvSet("MYVAR", "This is some text!")
    ; Retrieve the environment variable that was just assigned a value previously.
    Local $sEnvVar = EnvGet("MYVAR")
    ; Display the value of the environment variable $MYVAR%.
    MsgBox($MB_SYSTEMMODAL, "", "The environment variable %MYVAR% has the value of: " & @CRLF & @CRLF & $sEnvVar)
EndFunc   ;==>Example