CODE EXAMPLE FOR CSHARP

unity get distance between line and point

public Vector2 FindNearestPointOnLine(Vector2 origin, Vector2 end, Vector2 point)
{
    //Get heading
    Vector2 heading = (end - origin);
    float magnitudeMax = heading.magnitude;
    heading.Normalize();

    //Do projection from the point but clamp it
    Vector2 lhs = point - origin;
    float dotP = Vector2.Dot(lhs, heading);
    dotP = Mathf.Clamp(dotP, 0f, magnitudeMax);
    return origin + heading * dotP;
}