Add varibles to less files in gulp-plugin config options.
example:
var gulp = require('gulp');
var lessVars = require('gulp-add-less-variables');
gulp.task('less', function() {
gulp.src(lessFiles)
.pipe(lessVars({
var1: '10px',
var2: '20px',
var3: '30px'
}))
.pipe(less())
.pipe(concat('style.css'))
.pipe(gulp.dest('./public/css'));
});
var1, var2, var3
will be added at begin of file.