I'm trying to use assetic on windows and i like to configure the UglifyJS2 filter like this:

bin: "%%APPDATA%%/npm/node_modules/uglify-js/bin/uglifyjs"

On the command line this will be:

^%"APPDATA"^%"/npm/node_modules/uglify-js/bin/uglifyjs"

This is wrong, it should be:

"%APPDATA%/npm/node_modules/uglify-js/bin/uglifyjs"

I traced the problem down to this location:
https://github.com/symfony/symfony/blob/master/src/Symfony/Component/Process/ProcessUtils.php#L53

I understand the need to normalize to different environments. (Maybe linux does not need escaping for the % character?). In that case it could be an options to work with a list of "windows predefined environment variables" (use this search term in google).