How to pass parameters to a gulp task within the gulpfile

There is information out there, how to pass a parameter on a command line when running a gulp task. The example here shows how to pass a parameter from one task to another within the gulpfile.

Tested on Ubuntu 15.04 using node@4.4.2.

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'use strict'; /* * performs a build task of uglifying and concatenating txt files in the top subdirectories * the built files are deposited in build directory of each top subdirectory * * the challenge was in passing a variable to a task * * works with node@4.4.2, gulp (CLI version 1.2.1, Local version 3.9.1) * */ const gulp = require('gulp'); const fs = require('fs'); const path = require('path'); const concat = require('gulp-concat'); const uglify = require('gulp-uglify'); const notify = require('gulp-notify'); const _ = require('lodash'); const async = require('async'); // Function variable containing the processing task // ------------------------------------------------ // Process task needs to be performed on every given subdirectory. // For that the full path, that dynamically changes, is required. // The task is wrapped in a function, that accepts a subdirectory parameter, // which is then available to the task. // const subdirTask = (subdirPath, cb) => { // if the result is to live in ./build/${sundirectory} => get the subdirectory from the path // const basename = path.basename(subdirPath); // Define the processing task // -------------------------- gulp.task('process', () => { // selects files to act on return gulp.src(`${subdirPath}/*.txt`) // does what needs to be done .pipe(uglify()) .pipe(concat('all.txt')) // puts the result in the the specified place .pipe(gulp.dest(`${subdirPath}/build`)) // notifies that work was done .pipe(notify(`... Finished processing ${subdirPath}`)); }); // Now run the task // ---------------- gulp.start('process'); console.log(`\t\t\t\tprocessing ${subdirPath}`); cb(); }; // The main building task // ---------------------- // gets the parent directory // gets its top level subdirectories // asynchronously runs the actual processing task // gulp.task('build', () => { console.log('Hello world! Build me up!'); // Get parent directory // -------------------- let baseDir = process.env.baseDir || `${__dirname}/test`; baseDir = path.isAbsolute(baseDir) ? baseDir : path.join(__dirname, baseDir); console.log(`PARENT DIRECTORY = ${baseDir}`); // Asynchronously get the directory content // ---------------------------------------- fs.readdir(baseDir, (err, items) => { // retrieve only top lever subdirectories // use node-dir to get all nested directories let subdirs = _.filter(items, item => fs.statSync(`${baseDir}/${item}`).isDirectory()); // get subdirectory full paths subdirs = _.map(subdirs, item => `${baseDir}/${item}` ); console.log('PROCESSED SUBDIRS:'); console.log(subdirs); // Asynchronously run the process task for each subdirectory // --------------------------------------------------------- // async parameters: // subdirs ...... array of subdirectories to work on // subdirTask ... function variable, contains the work to be done // accepts two input parameters: // 1) subdirectory (provided implicitly by async) // 2) callback (provided as the third parameter to async.each) // callback ..... callback function, the second parameter for subdirTask // async.each(subdirs, subdirTask, (err) => { if (err) { console.error(err); } else { console.log(`Processing finished`); } }); }); }); // default task is run when the gulp command is issued on its own // -------------------------------------------------------------- gulp.task('default', ['build']);