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I have seen Setting and getting Windows environment variables from the command prompt?, but my question is slightly different.

Say I have a terminal program, myprogram.c -> myprogram.exe, which reads environment variables; say:

...
char *valueMYVAR = getenv("MYVAR");
printf("MYVAR is %s\r\n", (valueMYVAR==NULL)?"":valueMYVAR );
...

Now, if I'm in Linux bash, I can set the environment variable temporarily, just for that execution of the program, by simply writing it out on the command line, as in:

$ MYVAR=1 ./myprogram.exe

How could I do the same, if I am using the Windows Command Prompt (cmd.exe)? I have tried:

> SET MYVAR=1 myprogram.exe

... but it doesn't work - in the sense that myprogram.exe is not run at all, probably being interpreted as being part of the command line for the SET command.

Is this kind of a thing doable in Windows Command Prompt? If relevant, I use Windows 10.


EDIT: Found these:

Is there something like Command Substitution in WIndows CLI?

In Windows the '( )' operator has a similar behavior as the Bash command substitution.

https://stackoverflow.com/questions/8055371/how-do-i-run-two-commands-in-one-line-in-windows-cmd

Like this on all Microsoft OSes since 2000, and still good today:
dir & echo foo

So, I've tried:

> (SET MYVAR=1 && myprogram.exe)

... and this actually works - except, it seems the parentheses in Windows are not a "subshell" (or "subprocess"), and therefore setting the value "leaks" onto the current shell, which I don't want (in other words, if I just run myprogram.exe after the above command, it will still pick up MYVAR=1, whereas on Linux, MYVAR in that case would remain unset).

So, is there a way to do this on a single command line - and temporarily?

1
  • Thanks @Biswapriyo - that looks like it will work; though it would have been nice not to have to remember to "unset" the variable in the end
    – sdbbs
    Commented Feb 14, 2019 at 12:31

2 Answers 2

9

You could run a batch file with a setlocal

or on cmd line start another cmd.exe which inherits the current environment but changes are volatile.

cmd /c "SET MYVAR=1&myprogram.exe" 
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  • Thanks a lot @LotPings - the starting of another cmd.exe does exactly what I wanted (makes the environment variable changes not persistent)
    – sdbbs
    Commented Feb 14, 2019 at 15:58
4

Try this command:

set Foo=bar & abc.exe & set Foo=

This command does:

  1. Set Foo variable with bar value.
  2. Run abc.execommand.
  3. Unset Foo variable by adding blank value.
3
  • 2
    The ampersand (&) character is not allowed. The & operator is reserved for future use; wrap an ampersand in double quotation marks ("&") to pass it as part of a string. + CategoryInfo : ParserError: (:) [], ParentContainsErrorRecordException + FullyQualifiedErrorId : AmpersandNotAllowed Commented Oct 24, 2019 at 14:15
  • 1
    @KarlMorrison What do you mean by that? Are you using Command Prompt at all? This question is about in Command Prompt, not in Powershell.
    – Biswapriyo
    Commented Oct 24, 2019 at 14:36
  • That was using the command prompt I'm afraid! LotPings solution worked though. Commented Oct 25, 2019 at 7:41

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