What does `{,*/}` mean in paths of Gruntfile.js?

Question

In Gruntfile.js, I have got:

watch: {
    styles: {
      files: [
        '<%= yeoman.app %>/styles/{,*/}*.less'
      ],
      tasks: ['copy:styles', 'autoprefixer']
    }
}

For the path, what does {,*/} mean indeed? How does it differ to using double asterisks **/?

Frawley

Answer 1

This pattern is widely used in yeoman templates: it means to look only one level deep inside folder hierarchy. It is used mostly for performance reasons since watching too many files simultaneously can be slow (or even impossible).

Minton

Thanks for mentioning Yeoman specifically. Do you have a reference to the performance issues? – Think

Thanks for the reference, though it appears that the concern was more about the total number of file watches, irrespective of the depth of the directories. – Think

I guess so, but less depth => less files (generally). Anyway, I don't think this approach is any good, because it trades correctness for performance. – Minton

So, based on this, whats the difference between using {,*/} and /*/ as I tried the single * and it worked fine in my grunt concat script... – Rabblement

Can we use this pattern in grunt as well? – Arris

Answer 2

These are globbing patterns for Grunt, supported by the node-glob and minimatch libraries.

Basically:

• * matches any number of characters, but not /
• ** matches any number of characters, including /, as long as it's the only thing in a path part
• {} allows for a comma-separated list of "or" expressions

So, styles/{,*/}*.less matches the following files:

• LESS files inside styles directory
• LESS files inside direct sub-directories of styles directory (but no deeper)

Rowdyish

Thank you! Save 2 hours for me. ;) – Amero

Answer 3

I believe you're using a minimatch pattern there.

The double asterisk is a glob that causes recursion into subdirectories.

The single asterisk only matches 0 or more characters in the current directory (it matches every character except the slash character).

For example, a/**/d will match a/b/c/d.

Pycnidium

Answer 4

The answer is globbing-patterns .

The other answers had already answer what does{,*/}* mean.

But the different between **/ and {,*/}* is folder depth.

• /styles/{,*/}*.less has been divided into two situation

  1. /styles/*.less
  2. /styles/*/*.less

For example

/styles/{,*/}*.less will match /styles/x.less (situation 1)

/styles/{,*/}*.less will also match /styles/test/x.less (situation 2)

But /styles/{,*/}*.less can't match /styles/test/test1/x.less

But /styles/**/*.less can do that

Pressey