Introduction
I recently used the excellent Inno Setup utility to create some install scripts for my own applications. I discovered that there was no way to set a system-wide environment variable except by using an external application. SetEnv supports User and System environment variables.
I began by searching for the Microsoft setex tool, but couldn't find it. I didn't really try that hard though. I thought I'd write my own, hence this article.
You can find a proper setup kit for SetEnv on my website.
System Environment Variables
The method used to create a system-wide environment is dependent upon the operating system in use. SetEnv will automatically detect this and will use one of the following techniques to create/modify or delete environment variables.
Windows 95/98/ME
Under Windows 9x, creating an environment variable requires modifying the user's autoexec.bat file and then executing it or rebooting before the variable is recognized by the operating system. SetEnv will automatically locate the autoexec.bat file itself -- as long as the file is on the C:\ or D:\ drive -- and then add or modify the selected system variable. The one thing SetEnv will not do is reboot the PC, as it should be left up to the user or the Setup Kit -- from Inno Setup, for example -- to choose when to perform the reboot.
Windows XP/2000/2K3/Vista
Under more modern (i.e. proper) operating systems such as Windows 2000, XP, and Windows 2003 Server, environment variables are stored in the registry under the following key:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\
Control\Session Manager\Environment
Variables are added by creating a new value under this key or by modifying a value if it already exists. To delete a variable, we simply delete its registry value. That is, unless we are removing part of an expanded value such as PATH, in which case we only remove the part we want.
At this point, Windows will not be aware of our changes unless we log off or reboot. To get around this, SetEnv will broadcast a WM_SETTINGCHANGE to all of the Windows in the system. This allows other running applications such as Explorer.exe to be notified of our change. If you run SetEnv from a command prompt, then this will not update the environment variable for the current DOS window. This is mainly due to the fact that a process (SetEnv) cannot change the environment of its parent, the command prompt. However, any new DOS/command prompt that you open will show the new variable/value.
Broadcasting this message results in a slight delay of around 2-3 seconds, whilst the open Windows process it. So it may appear that SetEnv has hung, but this is not the case.
Using SetEnv
SetEnv is very easy to use and has only a few command line arguments. This section will describe how to use them. Typing SetEnv at a command prompt and then pressing the Return key will make SetEnv display its usage information. This can be seen in the screenshot at the top of this page.
User Environment Variables
As of version 1.04, SetEnv also supports User environment variables. If you want SetEnv to either add or delete a User variable, then add the -u option to the command line.
Creating a Variable
SetEnv can create two types of variables, a simple one that has only a single value such as:
InstallPath = C:\Program Files\Xanya\_Bin
... or more complex variables with multiple values. A good example of this is the PATH variable:
PATH = C:\WINDOWS\system32;C:\WINDOWS;C:\Program Files\Xanya\_Bin
To create a simple variable, just enter in the following command line. Obviously, substitute your own variable name and value:
SetEnv -a InstallPath "C:\Program Files\Xanya\_Bin"
Similarly, to add a variable with multiple values, you need to type the following command line for each value. Ensure that you prefix the value with the % character:
SetEnv -a name %value
E.g.
SetEnv -a PATH %"C:\Program Files\Xanya\_Bin
SetEnv -a PATH %"C:\Bin
To add a User variable instead of a System one, add the -u option as in the following example:
SetEnv -ua PATH %"C:\Program Files\Xanya\_Bin
Modifying an Existing Variable
You modify variables in exactly the same way in which you would create them. If you are modifying a multi-value variable and you forget the % prefix to the value, then SetEnv will automatically detect that the destination has multiple values and will modify it correctly.
Dynamic Variable Expansion
This allows you to set a variable to always equal the value of an existing environment variable, even if that variable changes. Let me show you an example of when this would be very useful. This example was inspired by Synetech; if you mind me stealing it just let me know.
Say that you have an environment variable called MEDIADIR (set to C:\Media) and you want to create two additional variables called MUSICDIR and PICDIR (set to %MEDIADIR%\Music and %MEDIADIR%\Pics, respectively). These would be expanded by the operating system to the following:
C:\Media\Music
C:\Media\Pics
Now, say you decided to move the MEDIADIR folder to drive D (D:\Media) using dynamic variable expansion. SetEnv will ensure that your MUSICDIR and PICDIR variables are correctly relocated to the following automatically.
D:\Media\Music
D:\Media\Pics
To enable dynamic variable expansion, simply create your variables as in the following example. Use the ~ symbol to identify the existing variable name.
setenv -a MEDIADIR C:\Media
// Create the original variable
// Create our dynamic variable, when MEDIADIR changes, so will MUSICDIR
setenv -a MUSICDIR ~MEDIADIR~/Music
// Our second dynamic variable, PICDIR will change if MEDIADIR changes
setenv -a PICDIR ~MEDIADIR~/Pics
Deleting a Variable
To delete a variable, specify the -d option instead of the -a option, as in the following example:
SetEnv -d InstallPath
To delete a value from a multi-value variable, you simply enter the following, specifying the value to remove:
SetEnv -d PATH %"C:\Program Files\Xanya\_Bin
As with modifying a multi-value variable, if you forget to specify the % prefix, then SetEnv will automatically work this out and delete the specified value only. To delete a User environment variable, simply add the -u option as follows:
SetEnv -ud PATH %"C:\Program Files\Xanya\_Bin
Running SetEnv from a Batch File
SetEnv can be run successfully from a batch file. However, a problem was found by David Langford, which occurs when you attempt to specify the expanded variable prefix % to a value which contains a drive letter, as in the following example. Note that this is only an issue when running SetEnv from a batch file:
SetEnv -d PATH %C:\Test
The Windows batch file interpreter will interpret the % character as a prefix to a variable. It will replace the character with what it believes is the variable %C: with the contents of that variable, which of course is nothing. This results in SetEnv being passed a modified value, as shown here:
SetEnv -d PATH \Test
This is obviously wrong, and SetEnv will not be able to match the value to be removed in the expanded variable. It will thus fail to delete the value from the variable. The workaround is to escape the % character with another % character. The following example will correctly remove the C:\Test value from the expanded variable, PATH.
SetEnv -d PATH %%C:\Test
Bugs
There are no known bugs, but if you do find any, then please let me know.
History
- 1.09 (Feb 9, 2008) - Fixed a problem on Windows 98 where it sometimes failed to open the Autoexec.bat file (Found by mulinux).
- 1.08 (May 31, 2007) - Updated
SetEnv's usage information on how to delete a user environment variable using SetEnv. The code has not changed.
- 1.07 (Jan 25, 2007) - Fixed a bug found by depaolim
- 1.06 (Jan 14, 2007) - Added dynamic expansion support (same as using
~ with setx), originally requested by Andre Amaral, additional request by Synetech.
- 1.05 (Sep 06, 2006) - Added support to prepend (rather than append) a value to an expanded
string, requested by Masuia.
- 1.04 (May 30, 2006) - Added support for User environment variables.
- 1.03 (May 17, 2006) - Updated the article to explain how to use
SetEnv from a batch file, after a problem was found by David Langford.
- 1.03 (Apr 20, 2006) - Bug fix in
ProcessWinXP() discovered by attiasr.
- 1.01 (Nov 15, 2005) - Bug fix in
IsWinME() discovered by frankd.
- 1.00 (Oct 29, 2005) - Initial public release
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 | Percent sign problems... [modified]
Sir Athos | 8:30 2 Feb '10 |
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Hi and thanks for this great utility!
I have a suggestion: it would be easier if the special meaning of a trailing "%" would be replaced by an option, such as "-e". The problem is, besides needing to escape it in batch scripts, that it creates confusion when trying to add a variable which is not an expanded variable, and its content starts with "%".
Example:
SetEnv -a MYSUBDIR=%MYMAINDIR%\sub
What do you think?
Edit: On second thought, I was confused. I was thinking of multi string registry entries instead of expanded variables. If your variable contains "%", it's very likely you'll want it to be an expanded variable. So, to put the above in a script, you'd write:
SetEnv -a MYSUBDIR=%%%%MYMAINDIR%%\sub
-=Athos=-
modified on Wednesday, February 3, 2010 6:43 PM
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Hi Athos,
Glad you like it and thanks for the suggestion - sorry about the confusion though 
If you do think of any new features let me know as I will be uploading a new version very soon.
regards,
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 | How to get the Newly changed environment settings to current process?
g_satish | 21:44 10 Jun '09 |
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I have sample which will set the environment variable and broadcast the message tat setting has been changed. Except the current process which set the environment variable all the other windows are getting the new change. How to get the new changed environment for the current process.
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Hi g_satish,
The problem is not with SetEnv but with Windows itself, it will not allow a process to modify the environment of it's parent process. This is why all the other windows will get an update, just not the one you call SetEnv from.
The only solution I am afraid is to start a new instance of the calling process.
Note (From the article):
SetEnv will broadcast a WM_SETTINGCHANGE to all of the Windows in the system. This allows other running applications such as Explorer.exe to be notified of our change. If you run SetEnv from a command prompt, then this will not update the environment variable for the current DOS window. This is mainly due to the fact that a process (SetEnv) cannot change the environment of its parent, the command prompt. However, any new DOS/command prompt that you open will show the new variable/value.
Hope this helps,
regards,
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| Date Variables
Gerard Nicol | 11:02 11 Feb '08 |
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It is always a pain to set dates as environmental variables.
While you are at it you should add the ability to create variables with a strftime-like syntax.
say:
SetEnv -a today 0 "%Y-%d-%m"
SetEnv -a tomorrow +1 "%Y-%d-%m"
Gerard
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Hi Gerard,
Actually I think that's a really good idea and will try to get round to implementing it in the next week.
thanks
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| Version 1.09
Jonathan [Darka] | 2:04 10 Feb '08 |
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Version 1.09 should be uploaded in the next day or so and fixes a bug on Windows 98 where it would fail to open the Autoexec.bat file sometimes due to incorrect file permissions.
If any other issues are found then please let me know and I will fix them as soon as I can.
Latest version is always available from my web site, SetEnv[^].
regards,
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| Setenv bust under win98
mulinux | 9:41 6 Jan '08 |
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Works fine under XP however under win 98 which ever option you use always gives
"Error - Open Autoexec.bat : The Parameter is incorrect"
Setenv correctly identifies OS and finds Autoexec.bat on which ever drive I place it (and gives correct not found error if autoexec doesn't exist).
Can't force error 5 access denied even if making autoexec read only so looks like setenv falling over on initial opening of autoexec. My C++ not good enough to figure it out. Bug or me being stupid ?
Many thanks
Dave
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Hi Dave,
Thanks for the update, I will check it out and get back to you but it might be a day or so as we've all been made redundant here and I have to get my CV up to date.
regards,
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Many thanks Jonathan.
I've been in same situation for 5 months here so know exactly how you feel.
Dave
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Thanks for understanding,
I should get time on Monday to look at this as I will be a little busy the rest of the week as I am flying to the US (Arizona) on Thursday to "transfer knowledge" to the US developers that are part of the company I work for.
reagards,
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Hi Dave,
Finally had time to fix it, it was a permissions problem with the CreateFile() call.
Thanks for reporting it though, I'd have never spotted it myself as I don't use Windows 98 anymore.
I had to hunt down a copy of 98 which is why it took me so long to fix, sorry about that.
I have updated the CodeProject article but that will take a day or so toget posted, in the meantime you can get the latest version from my own website[^].
regards,
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| Strange issue using backslash and dbl quote [modified]
Freddy999 | 17:55 13 Oct '07 |
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I have a strange issue with the following:
command: setenv -a myvar "my path\"
result : myvar = my path"
Surprise: the saved value ends with a double quote, and the backslash disappeared, thus it acts as escape char. This happens on W2003.r2 and on XP.sp2, with both SETENV and SETX, thus is it rather a Windows issue? Or do I do something wrong?
P.S. I did not find a way to use the above %myvar% in an IF or a FOR command. It always results in a script error.
Freddy
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 | Re: Strange issue using backslash and dbl quote
Jonathan [Darka] | 22:00 14 Oct '07 |
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Hi Freddy,
You need to escape the backslash character, try this:
setenv -a myvar "my path\\"
regards,
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Jonathan,
thanks - this resolves it.
Are there other combinations of characters in which the BS is interpreted as escape char?
Best, Freddy
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You basically have to backspace any character that you do not want the shell to process, such as double quotes, etc.
regards,
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| Same code under VB
McGoldi | 7:27 8 Jun '07 |
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Hi. I'm trying to just send the Broadcast "SendMessageTimeout" but I don't know the value for
(LPARAM) "Environment"
In my Examplecode it's just 0, but that doesn't work! Can you help?
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Ok, I just found out, that the "SendMessageTimeout" from the lib "user32" can also take a string as LPARAM, with just can be set to "Environment" and it works!
Thanx anyway!
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| Delete a User Variable [modified]
JTAnderson | 17:20 11 Apr '07 |
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I don't know if this is intentional or not, but when I do this:
setenv -ua TEST variable
setenv -d TEST
It does not remove it. Works fine if it is a system variable but not a user variable.
-JT
-- modified at 22:33 Wednesday 11th April, 2007
Actually, I just found the -ud functionality. Might want to put that in the usage. Thanks.
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Thanks JT,
I will modify the usage information and update the article as soon as I can.
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I'm uploading a new version tomorrow with the new usage information.
regards,
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| Problem with empty value
depaolim | 4:12 25 Jan '07 |
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great and usefull work Jonathan
I have found a little and subtle problem, try this:
SetEnv.exe -uap path %TEST4
SetEnv.exe -ud path %TEST4
via regedit in HKEY_CURRENT_USER\Environment\path you find an empty value. Ok.
But if you look at user environmente variables, via System Properties Dialog, you find a strange value that results to be equal to the very next variable (in my case "TEMP") ... and this is the same value you see when you give a "path" command via cmd prompt.
It seems to be a problem of Windows RegSetValueEx
I have found the following work-around: delete the key if the value is empty
Main.cpp:332 pseudo-code
if(szNewValue.empty())
obKey.DeleteKeyValue ...
else
SetRegistryKey
what do you think about? have you any better idea?
regards,
Marco
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Hi Marco,
Glad you like it and appreciate the bug report .
It's also very cool of you to produce a workaround , thank you.
I have just tested this (very briefly, i.e. once) on Win XP and cannot reproduce it (typical really).
What OS are you using ?
regards,
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XP Pro with Windows Update
I have reproduced on another desktop too
(... it is not clear where the new "ghost" value comes from, in this case the first variable value)
bye
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Hi Marco,
I have now reproduced it and shall apply your fix tonight.
I don't have the code here so cannot say why its happening but your fix is fine, I shall investigate a little tonight when I fix it.
I will have a new version on my website tonight and shall update codeproject as soon as I can.
thanks again for spotting it.
best wishes,
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Last Updated 11 Feb 2008 |
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