Set And Setx

Everybody knows to use set to set environment variable values.  And I guess everybody should know setx.  The crucial differences between set and setx are:

• set takes effect in local cmd context.  Meaning once you exit or close the cmd window, you lose the environment variable.
• setx takes effect in future cmd context.  So you won't see the environment variable and its value in the current cmd.  You need to open a new cmd window to see it.

This really leads to one obvious conclusion: always use set and setx side by side if you want to set something globally but you want to see it in effect immediately.

A good example is if you want to set an environment variable containing your current IP address.  You would do something like this:

ipconfig | findstr IPv4 > %TEMP%\ipaddress.out

REM This will give you something like this

REM IPv4 Address. . . . . . . . . . . : 192.168.1.3

REM You then parse the output file, taking the second token after splitting at the ":"

for /F "delims=: tokens=2" %i in (%TEMP%\ipaddress.out) do (

    set IPADDR=%i

)

REM Then remove the spaces

set IPADDR=%IPADDR: =%

REM Then to persist this in the system environment, you call setx.

setx /M IPADDR %IPADDR%

Now of course setx is much more powerful than simply calling it the way I did in the above example.  Take a look at setx /? to see the complete options.  For example the above usage can also be done using setx alone.

ipconfig | findstr IPv4 > %TEMP%\ipaddress.out

REM Then you use setx to read its value from a file, keying in on a string,

REM and get the value relative to that string. In this case we key in on the ":"

REM and get the token after that.  And setx coordinates start at 0, not 1.

setx /M IPADDR /F %TEMP%\ipaddress.out /R 0,1 ":"

The reason I hardly ever use this is because most of the time I need the environment variable defined in the current context first, and then also persisting it for future cmd contexts.   The second example above only does it for future context.