What is the best way to use vcvars?

[doctorpangloss]

Since the busybox environment isn't mingw, it is suitable for native build tools as though it were cmd but a better shell.

Any opinions how to use the scripts with busybox?

[garoto]

say again?

[doctorpangloss]

lots of build tooling expects environment variables set using vcvars*.bat a set of utilities from the Visual Studio toolchain:

https://learn.microsoft.com/en-us/cpp/build/building-on-the-command-line?view=msvc-170

My question is how to do this in the context of the busybox shell.

[rmyorston]

To run a shell in the context created by running a batch file you could do something like:

~ $ cmd /k "whatever.bat & busybox sh & exit"

Or more concisely:

~ $ cmd /c "whatever.bat & busybox sh"

[doctorpangloss]

for future reference:

cmd /c 'C:\PROGRA~2\MICROS~2\2022\BUILDT~1\VC\AUXILI~1\Build\VCVARS~1.BAT amd64 & busybox sh -ilX'

[doctorpangloss]

How would I do this in a .profile? @rmyorston

[ale5000-git]

The .profile file is a shell script, just put the shell code inside it.
Inside the .profile you could just put:
'C:\PROGRA~2\MICROS~2\2022\BUILDT~1\VC\AUXILI~1\Build\VCVARS~1.BAT' amd64
PS: I suggest to use the long name, not the dos name.

Then when executing busybox ash -l it automatically execute the .profile file.

[doctorpangloss]

the side effects of the vcvars script are not applied to the currently running shell

here was what I ultimately added:

temp_file=$(mktemp)

cmd /c 'C:\PROGRA~2\MICROS~2\2022\BUILDT~1\VC\AUXILI~1\Build\VCVARS~1.BAT amd64 && set' | 
sed '1,5d' | 
while IFS= read -r line
do

    line=${line%$'\r'}
    

    [ -z "$line" ] && continue
    

    key=${line%%=*}
    value=${line#*=}
    

    case "$key" in
        *[!a-zA-Z0-9_]*) continue ;;
    esac
    

    value=$(echo "$value" | sed 's/[\\()$`]/\\&/g')
    

    echo "export $key=\"$value\"" >> "$temp_file"
done

echo "export CC=cl" >> "$temp_file"
echo "export CXX=cl" >> "$temp_file"

. "$temp_file"

rm "$temp_file"

[ale5000-git]

It is difficult because I don't have a vcvars file at hand.
Could you please post the file so I can look at it better?

[rmyorston]

I can't think of anything better than what you're doing: running the batch file and listing the resulting environment in a format suitable for import to the shell.

One minor improvement would be to run cmd.exe in a reduced environment (as far as possible, see #426) so we (mostly) just need to process newly set variables. This appears to do the trick:

env -i COMSPEC="$COMSPEC" PATH="$PATH" cmd /c ...

I'm also not sure about the sed '1,5d': in my testing it was necessary to remove fewer lines. But that might just be because my test didn't reflect what vcvars actually does.

[rmyorston]

A different approach:

temp_file1=$(mktemp)
temp_file2=$(mktemp)
temp_file3=$(mktemp)

cmd /c 'vcvars.bat >nul & busybox sh -c export' | sort >"$temp_file1"

export | sort >"$temp_file2"

comm -2 -3 "$temp_file1" "$temp_file2" | grep -v 'SHLVL=' >"$temp_file3"

. "$temp_file3"

export CC=cl
export CXX=cl

rm "$temp_file1" "$temp_file2" "$temp_file3"

Instead of using set from cmd.exe to get the new environment use the shell's export built-in. This produces output in a form that can be sourced.

Use comm to compare the environment generated by vcvars.bat with the current environment. The result should be a file listing only the variables which have been changed or added by vcvars.bat. Source that.

Add error checking to taste. Use at your own peril.

[doctorpangloss]

I am observing that both our approaches produce errors when compiling the Python package flash_attn on Windows, whereas my original snippet cmd /c 'C:\PROGRA~2\MICROS~2\2022\BUILDT~1\VC\AUXILI~1\Build\VCVARS~1.BAT amd64 & sh -ilX' does not. I am investigating.