How to draw lines in Unity

There are a couple of wrinkles to rending lines in Unity depending on what you are trying to do.  Line rendering is achieved with the LineRenderer.  A Game Object can only have a single LineRenderer attached so you need to create a new GameObject for each LineRenderer.  If you need to dynamically create and destroy lines you'll need to keep track of them in a list.

 //have to add a new game object per line renderer
 LineRenderer lineRenderer = new GameObject().AddComponent<LineRenderer>();

The other issue is that if your lines are using a shader that isn't referenced anywhere else in your scene, the Unity Editor won't include them in your package and the lines won't render in a build project although they will work in the editor.

 // force the shader to be copied into the resource folder using
// Edit->ProjectSettings->Graphics->Always Included Shaders 
Material whiteDiffuseMat = new Material(Shader.Find("Unlit/Color")); 
lineRenderer.material = whiteDiffuseMat;

Not completely horrible but still, hoops to be jumped through...

using UnityEngine;
using System.Collections;

public class basicRender : MonoBehaviour {
    
    void RenderCircle(Vector3 pos, float rad, Color col)
    {
        float angle = 0.0f;
        int segments = 128;
    
        //have to add a new game object per line renderer
        LineRenderer lineRenderer = new GameObject().AddComponent<LineRenderer>();

        // force the shader to be copied into the resource folder using Edit->ProjectSettings->Graphics->Always Included Shaders 
        Material whiteDiffuseMat = new Material(Shader.Find("Unlit/Color")); 
        lineRenderer.material = whiteDiffuseMat;

        lineRenderer.SetColors(new Color(1.0f,1.0f,1.0f,1.0f), new Color(1.0f,1.0f,1.0f,1.0f));
        lineRenderer.SetWidth(0.02F, 0.02F);
        lineRenderer.SetVertexCount(1+segments);

        for (int i = 0; i < (segments + 1); i++)
        {
            Vector3 p = new Vector3();
            p.x = pos.x + (Mathf.Sin (Mathf.Deg2Rad * angle)*rad);
            p.y = pos.y + (Mathf.Cos (Mathf.Deg2Rad * angle)*rad);
            p.z = pos.z;
            lineRenderer.SetPosition (i,p);
            angle += (360.0f / segments);
        }
    }

    // Use this for initialization
    void Start () 
    {
        float r = 0.6f;

        for (int i = 0; i<20; i++) 
        {
            RenderCircle(new Vector3(0.0f,0.0f,0.0f),r,new Color(1.0f,1.0f,1.0f,1.0f));
            r+=0.6f;
        }
   }
    
    // Update is called once per frame
    void Update () 
    {
    if (Input.GetKeyDown(KeyCode.Escape)) Application.Quit();
    }


    private void OnDestroy()
    {
        Destroy(this.GetComponent<Renderer>().material);
    }
}