Path.Combine(string, string)

Description

Concatenates two path strings.

If path1 does not end with a valid separator character DirectorySeparatorChar is appended to path1 prior to the concatenation.

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

public class ExampleClass : MonoBehaviour {
    void Start() {
        Debug.Log(Path.Combine("/First/Path/To", "Some/File/At/foo.txt"));
    }
}