Edges-only shader for cube-like things

gistfile1.txt

Shader "Custom/EdgesOnly"
{
	Properties
	{
		_EdgeColor ("Edge Color", Color) = (1,1,1,1)
		_EdgeWidth ("Edge Width", Range(0, 0.3)) = 0.1
	}
	SubShader
	{

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			
			#include "UnityCG.cginc"

			struct appdata
			{
				float4 vertex : POSITION;
				float2 uv : TEXCOORD0;
			};

			struct v2f
			{
				float2 uv : TEXCOORD0;
				float4 vertex : SV_POSITION;
			};

			fixed4 _EdgeColor;
			float _EdgeWidth;
			
			v2f vert (appdata v)
			{
				v2f o;
				o.vertex = UnityObjectToClipPos(v.vertex);
				o.uv = v.uv;
				return o;
			}
			
			fixed4 frag (v2f i) : SV_Target
			{
				fixed4 col = (i.uv.x < _EdgeWidth || i.uv.x > 1-_EdgeWidth || i.uv.y < _EdgeWidth || i.uv.y > 1-_EdgeWidth) ? _EdgeColor : (0,0,0,0);
				return col;
			}
			ENDCG
		}
	}
}