Question

I want to determine what the PATH environment variable was after I execute a batch file (vcvarsall.bat) by running

cmd /c "vcvarsall.bat x86_amd64 && echo %PATH%"

but what happens is not what I expect. For example, if I run:

cmd /c "set PATH=test && echo %PATH%"

I just get the PATH of the host process, not “test” as I expected, as echo %PATH% should be running in the context of the child process, not the parent. So, why does this happen, and how do I go about getting the result I’m after?

Answer 1

cmd /c "set PATH=test && echo %PATH%"

will interpret PATH before it’s changed. This is actually a neat trick to export environment variables outside of a setlocal/endlocal chunk with:

ste xyzzy=twisty
startlocal
set xyzzy=plugh
endlocal && set xyzzy=%xyzzy%

Normally (without the && xyzzy=... bit, the xyzzy variable would still be the initial value of twisty after the block but the fact that the %xyzzy% is interpreted before the entire endlocal line while the set is actioned after the endlocal command, allows you to export the change.

If you want to interpret a variable after the set, you need delayed expansion:

cmd /v:on /c "set PATH=test && echo !PATH!"

The /v:on turns on delayed expansion and the use of ! instead of % indicates that you want to use that delayed expansion.