Sign Up for Free

RunKit +

Try any Node.js package right in your browser

This is a playground to test code. It runs a full Node.js environment and already has all of npm’s 400,000 packages pre-installed, including catw with all npm packages installed. Try it out:

var catw = require("catw")

This service is provided by RunKit and is not affiliated with npm, Inc or the package authors.

catw v1.0.1

concatenate file globs, watching for changes


concatenate file globs, watching for changes

This module is just like the cat command, but with watching!

build status


#!/usr/bin/env node

var catw = require('catw');
var fs = require('fs');

catw('*.txt', function (stream) {
    var w = stream.pipe(fs.createWriteStream('/tmp/bundle.txt'));
    w.on('close', function () { console.log('wrote to /tmp/bundle.txt') });

If we run the program in a directory with files a.txt and b.txt, the bundle.txt output will be both files concatenated together (in string-order by filename):


If we edit a.txt to be "BEEP" instead of "beep", the bundle.txt is now:


and then if we add a third file c.txt with the contents "!!!", the output is now:


We can even delete files. If we delete b.txt, the output is now:


If we add a new file called bloop.txt with contents "BLOOP", the bundle.txt output is now:


because the glob expansions of directories are sorted before concatenating.


There is a command-line catw command that ships with this package.

usage: catw {OPTIONS} [FILES...] -o OUTFILE

  If FILES is "-", read from stdin.
  If there is no OUTFILE, write to stdout and exit without watching.


    -w, --watch      Watch for changes.
                     Default: true except when writing to stdout.
    -c, --command    Execute a transform command for file before concatenating.
                     The env var $FILE will be set for each file path.
    -t, --transform  Transform each file using a module.

    -v, --verbose    Print the number of bytes written whenever a file changes.

    -h, --help       Print this help message.

Make sure to escape the globs that you want `catw` to watch so your shell won't
expand them.


var catw = require('catw')

var cat = catw(patterns, opts={}, cb)

Create a new cat to concatenate patterns, an array of strings or a single string and watch each of the patterns for changes: new files, deleted files, and file updates.

It is false, don't watch for changes, only concatenate once.

You can pass in a opts.transform(file) function that returns a transform stream to modify file contents before the contents are written to the bundle.

If specified, cb(stream) sets up a listener on the 'stream' event.


Stop listening for updates to the patterns.


cat.on('stream', function (stream) {})

Each time a file matched by a pattern changes or there is a new or deleted file matched by a pattern, this event fires with a stream that will output the concatenated file contents.


To get the module, with npm do:

npm install catw

and to get the catw command do:

npm install -g catw


With npm do:

npm test



RunKit is a free, in-browser JavaScript dev environment for prototyping Node.js code, with every npm package installed. Sign up to share your code.
Sign Up for Free