How to get the file if I know the root directory and relative path?

Question

In Dart, if I know the root directory and the relative path of a file, how to create a file instance for it?

Directory root = new Directory("/root");
String relativePath = "logs/users.log";

How to create a file instance for the users.log?

In java, it's very simple:

new File(root, relativePath);

But in Dart, I can't find a simple solution as that.

This is not possible in Dart SDK. You must use third-party software. Even Dart SDK uses external packages for this purpose. This fact looks very strange that Dart SDK does not have even simplest support of this feature natively. In this case this means that you cannot write (single file command line) scripts in Dart language because this requires that you use other packages. Of course, you can compile your application (root script and their dependencies) into snapshot but this is not the same as you wrote it as a (single file) command line script with readable source code. — mezoni, Mar 03 '14 at 15:04

Günter Zöchbauer · Accepted Answer · 2016-03-21T10:38:01.607

7

This is the simplest solution I found

import 'package:path/path.dart' as path;

...

String filePath = path.join(root.path, relativePath);
filePath = path.normalize(filePath);
File f = new File(filePath);

edited Mar 21 '16 at 10:38

answered Mar 03 '14 at 14:26

Günter Zöchbauer

623,577
216
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1,567

score 2 · Answer 2 · edited Jun 20 '20 at 09:12

2

Joining `/home/name/` and `../name2` to yield `/home/name2`

Edit:

Thank you Günter Zöchbauer for the tip.
It seems linux boxes can handle a path like /home/name/../name2.

On a windows machine, Path.normalize needs to be used and the extra / Path.normalize preppends at the head must be removed.

Or use new Path.Context():

import 'package:path/path.dart' as Path;
import 'dart:io' show Platform,Directory;

to_abs_path(path,[base_dir = null]){
  Path.Context context;
  if(Platform.isWindows){
    context = new Path.Context(style:Path.Style.windows);
  }else{
    context = new Path.Context(style:Path.Style.posix);
  }
  base_dir ??= Path.dirname(Platform.script.toFilePath());
  path = context.join( base_dir,path);
  return context.normalize(path);
}

edited Jun 20 '20 at 09:12

Community

1
1

answered Mar 21 '16 at 10:21

TastyCatFood

1,632
1
15
27

1

`path.join()` works fine for me with relative paths. If you want to get rid of `../`, just call `relativePath = path.normalize(relativePath);`. See also my updated answer. – Günter Zöchbauer Mar 21 '16 at 10:38
Hi, Günter Zöchbauer. Thanks for the useful tip. It was a platform issue. `new Path.Context` seems the cleanest solution. – TastyCatFood Mar 21 '16 at 14:35
Wasn't aware of `Context`. Thanks for sharing :) – Günter Zöchbauer Mar 21 '16 at 14:37

score 0 · Answer 3 · answered Jul 26 '19 at 20:14

I found that problem to find relative path of a file inside of my test script file, so I improved the answer of @TastyCatFood to work in that context too. The following script can find the relative of a file every where:

import 'dart:io';
import 'package:path/path.dart' as path;

///  Find the path to the file given a name
///  [fileName] : file name
///  [baseDir] : optional, base directory to the file, if not informed, get current script path.
String retrieveFilePath(String fileName, [String baseDir]){
  var context;
  // get platform context
  if(Platform.isWindows) {
    context = path.Context(style:path.Style.windows);
  } else {
    context = path.Context(style:path.Style.posix);
  }

  // case baseDir not informed, get current script dir
  baseDir ??= path.dirname(Platform.script.path);
  // join dirPath with fileName
  var filePath = context.join(baseDir, fileName);
  // convert Uri to String to make the string treatment more easy
  filePath = context.fromUri(context.normalize(filePath));
  // remove possibles extra paths generated by testing routines
  filePath = path.fromUri(filePath).split('file:').last;

  return filePath;
}

The following example read the file data.txt in the same folder of main.dart file:

import 'package:scidart/io/io.dart';

main(List<String> arguments) async {
   File f = new File('data.txt');
}

How to get the file if I know the root directory and relative path?

3 Answers3

Joining /home/name/ and ../name2 to yield /home/name2

Edit:

Joining `/home/name/` and `../name2` to yield `/home/name2`