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7.1.1 • Public • Published


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Fast, rule based, file system transformations.

Basic Usage

Using fs-transform is fairly straight forward, here's an example that illustrates its core features:

// 1. Require the transformer class
var Transformer = require('fs-transform');
// 2. Define an array of transform rules
var rules = [
  // 2.1 Copy files
    action: 'copy',
    source: 'source/file',
    dest: 'dest/file'
  // 2.2 Rename files
    action: 'rename',
    source: 'source/file',
    dest: 'dest/file'
  // 2.3 Exclude files from all subsequent searches
    action: 'exclude',
    files: ['A.txt', 'B.dmg']
  // 2.4 Search and Replace in Files
  //     Note: this is applied globally to all files in the root directory
    action: 'replace',
    search: 'foo',
    replace: 'bar',
    // Use `exclude` property to define a set of files to exclude for this
    // search and replace
    exclude: [
// Execute the transformation on the given root directory (/root/path)
Transformer.transform('/root/path', rules, function (err) {
  // Handle errors if they arise, and move on!

Rule Actions

fs-transform ships with three basic transform rule implementations, or actions, they are:

  1. copy - Copies a file
  2. rename - Renames a file
  3. replace - Performs a global search and replace (without regex)

If you need custom transformations, you can easily add them by using a Transformer instance, like so:

var Transformer = require('fs-transform');
// 1. Instantiate a new transformer with a root directory and rules
var transformer = new Transformer('/root/dir', rules);
// 2. Add a custom rule action implementation
transformer.setAction('custom-action', function (rule, cb) {
  // This function will be applied to the `transformer` object itself;
  // which means you can use Transformer prototype methods directly, like this:
  this.addWarning(rule, 'Foo does nothing').
  // When you are done with handling your action, make sure to execute
  // the callback.
  if (rule.errorOut) {
    cb(new Error('Foo failed.'));


The library is fairly intelligent about when and how to apply transforms. For instance, if you attempt to perform a rename but the source file doesn't exist the library will skip that rule and issue a warning.

After a transformation completes you can access all of the warnings generated by the library like so:

Transformer.transform('/root', rules, function (err, transformer) {
  // Look here for a list of all the warnings
  var warnings = transformer.warnings;
  // Each warning will have both a `rule` and a `message` field so you can
  // narrow down why the warning occurred.

Below is a complete listing of the warnings that can be generated during a transform pass, by rule type:

Copy & Rename

Copy and rename perform the same checks and have the same behavior when issuing warnings. The warnings, in order of precedence, are:

  • 'Missing source file.' - if the rule.source was not a string.
  • 'Missing destination file.' - if the rule.dest was not a string.
  • 'Source file does not exist.' - if the given path to the source file did not exist on the filesystem.
  • 'Overwriting destination file.' - if the given destination file exists and has been overwritten by the operation.


  • 'Search pattern not specified.' - The given was not a string.
  • 'Replacement not specified.' - The given rule.replace was not a string.
  • 'Excludes not supplied as an array, omitting.' - The given rule.exclude was given, but it was not an array, and will thus be ignored.
  • 'Search did not return any results.' - The given could not be found in any file under the root directory.
  • 'Unused exclude.' - An exclude was given that was never used to exclude a file from the search.
  • 'All results were excluded.' - The given set of excludes ended up removing all of the files from the search results.

Dry Runs

fs-transform performs all of its work in a temporary directory so it can gracefully fail if an error occurs (leaving the root directory as it was before the transforms were applied).

For further safety you can perform transformations in "dry run mode". Using it is rather simple:

Transformer.dry('/root/directory', myRules, function (err, transformer) {
  // Two things to not:
  // 1) Check to see if errors are reported in `err`
  // 2) The `transformer` now has all the same information as it would during
  // an actual run!

Generating Diffs

fs-transform allows you to get a full recursive diff between the root before transformations were applied, and the root after. Here's an example of how to get the full text diff:

Transformer.dry('/root/directory', myRules, function (err, transformer) {
  // Get and log the diff:
  var fullDiff = transformer.getDiff();


If you'd like to contribute to the library please abide by the following rules:

  1. Make sure to compile and read the jsdoc documentation (run npm run doc, then open'doc/index.html' in a browser).
  2. Ensure all existing tests pass (run npm test).
  3. If you add new functionality, please add new tests and ensure 100% coverage.
  4. Make sure you handle all warning corner-cases (see the source for examples of how the existing actions)
  5. Update the jsdoc if you make changes to the any of the method behaviors.
  6. Please submit a PR that clearly defines the purpose of your contributions




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