fs.readdir - optional filter

[Christian Joudrey]

Hey guys,

I don't know if this was brought up, but it would be interesting to be
able to filter the files that are returned when reading a directory.

Something along the lines of:

fs.readdir(path, callback)

and

fs.readdirSync(path, filter)

The filter could be either a String or an instance of RegExp.

This would allow us to easily filter files that are returned as such:

fs.readdir("/home/chris", function() { }, "*.txt")

or

fs.readdir("/home/chris", function() { }, /\.txt$/i)

Thoughts?

- Chris

[Christian Joudrey]

Edit: I meant fs.readdir(path, [callback], [filter]) and
fs.readdirSync(path, [filter])

[Isaac Schlueter]

I wouldn't mind something like this, but:

a) the filter should go before the cb, not after. In node, the cb is
always the last arg.
b) the function shouldn't be called "readdir". The methods on the fs
module map directly to their "man 3" counterparts, so this function
maps pretty directly to the semantics of readdir(3).

--i

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[Ricardo Tomasi]

This can be done in userland without any hassle:

fs.readdirSync('/home/chris').filter(function(v){ return /
\.txt/.test(v); });

[Christian Joudrey]

@Isaac Schlueter: I agree, in fact I think this should be a new
function, but didn't know what to call it.

@Ricardo: Of course you can, but if you can do that processing at the
time of reading the folders contents it would likely be faster. No
point in building up a big array of things that you won't use. I
understand your point tho.

[Dominic Tarr]

unless you are trying to ls directories with thousands of files thousands of times you probably have bigger problems someplace else.

what is your usecase?

[Christian Joudrey]

To be honest, I am not dealing with thousands of files.

I just think providing fs.filterdir and fs.filterdirSync would
simplify the JS code (not having to .filter the return) and avoid
allocating the entries in the array for no reason.

We could even add a second option for filtering whether only dirs or
only files should be returned.

fs.filterdir(dir, filter, [type = FILTER_TYPE_FILES |
FILTER_TYPE_DIRECTORY], [callback])

and

fs.filterdirSync(dir, filter, [type = FILTER_TYPE_FILES |
FILTER_TYPE_DIRECTORY])

This would easily allow something like this:

fs.filterdir('/tmp', /*\.txt$/i, FILTER_TYPE_FILES, function(err,
files) {

});

Thoughts?

On Mar 14, 10:22 am, Dominic Tarr <dominic.t...@gmail.com> wrote:
> unless you are trying to ls directories with thousands of files thousands of
> times you probably have bigger problems someplace else.
>
> what is your usecase?
>

[Isaac Schlueter]

Actually, adding a "filtertype" flag that could be either directories
or files would make readdir a lot slower, since it'd have to stat
everything in the directory. Then there's the question of whether it
should use stat or lstat (ie, is a symlink to a directory interpreted
as a directory or a file?)

The more I think about this, I really think this belongs outside of
node core. There are a lot of edge cases to consider.

[Christian Joudrey]

Yeah I don't think it should be in `readdir` either, which is why I
suggested `fs.filterdir`.

The idea was to offer a built-in way to easily filter through a
directory's contents like in Ruby: Dir["*.txt"].

I suppose I will code it up in JS for the moment instead.

[Pau]

+1 to keep this in "userland"

ls | grep '.txt'

[Isaac Schlueter]

Dir["*.txt"] can be done pretty easily today.

npm install glob
require("glob").glob("*.txt", function (er, files) { ... })
or:
files = require("glob").globSync("*.txt")

[Christian Joudrey]

Wow!

Well to that I say:

One day, in <Node.js Mailing List>:
[3:55pm] Christian Joudrey: it would be good to have a file system
Glob functionality (to get an array of filenames)

Thanks a bunch!