Can Gulp change LESS variables?

Question

I'm looking to toggle IE8 mode in my LESS files and automated the file generation in Gulp.

This is where I stopped in what to pass gulp-less (minus a bunch of stuff):

var IE = true;

var LESSConfig  =  {
        plugins: [ ... ],
        paths: LESSpath,
        ie8compat: IE,  //may as well toggle this
        // Set in variables.less, @ie:false; - used in mixin & CSS guards
        // many variations tried
        // globalVars: [ { "ie":IE } ], 
        modifyVars:{ "ie":IE }
    };

...

.pipe( less ( LESSConfig ) )

Is variable modification not supported in Gulp?

I'd like to avoid using gulp-modify et al if I can. I'd like to keep the build system fairly abstracted from the source files.

Answer 1

modifyVars is working for me now:

    ...

    var LESSConfig = {
        paths: paths.LESSImportPaths,
        plugins: [
            LESSGroupMediaQueries,
            LESSautoprefix
        ],
        modifyVars: {
            ie: 'false'
        }
    };

    var LESSConfigIE = {
        paths: paths.LESSImportPaths,
        modifyVars: {
            ie: 'true'
        }
    };

    function processLESS (src, IE, dest){
       return gulp.src(src)
         .pipe( $.if( IE, $.less( LESSConfigIE ), $.less( LESSConfig ) ) )
         .pipe( $.if( IE, $.rename(function(path) { path.basename += "-ie"; }) ) )
         .pipe( gulp.dest(dest) )
    }

    // build base.css files
    gulp.task('base', function() {
         return  processLESS( paths.Base + '/*.less', false, paths.dest );
    });

     // build base-ie.css files for IE
     gulp.task('baseIE', function() {
         return  processLESS( paths.Base + '/*.less', true, paths.dest );
     });