packageRoot property
String packageRootThe --package-root flag passed to the executable used to run the script in this isolate.
If present, it specifies the directory where Dart packages are looked up.
Is null if there is no --package-root flag.
Source
static String get packageRoot => _Platform.packageRoot;
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Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
https://api.dartlang.org/stable/1.24.3/dart-io/Platform/packageRoot.html