Path.GetDirectoryName()

説明

指定されたパス文字列のディレクトリ名を返します

The string returned by this method consists of all characters between the first and last DirectorySeparatorChar or AltDirectorySeparatorChar character in the path. The first separator character is included, but the last separator character is not included in the returned string.

using System.IO;
using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void Start() {
        Debug.Log(Path.GetDirectoryName("/Path/To/A/File/foo.txt"));
    }
}