To create enemy bullet when player is come close enough :
Code:

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var shoot_speed = 5;
var pushValue;

function shoot_you()
{
   pushValue += 0.1;      // prevent bullet hit each other
   my.push = pushValue;   // reset it if reached certain value
   my.skill1 = 100;       // bullet life
   while(my.skill1 > 0)
   {
      c_move(my,vector(shoot_speed*time_step,0,0),nullvector,Ignore_Push);
      my.skill1 -= 1 * time_step;
      wait(1);
   }
   ent_remove(my);
}

Action Spawn2 // enemy action
{
   c_setminmax(my);
   while(player==NULL) {wait(1);}
   while(my)     
   {
       if (vec_dist(player.x,my.x) < 50)
       {
          you = ent_create(bullet,vector(my.x-40,my.y,my.z),shoot_you);
          you.pan = my.pan;
       }
       wait(-0.5);
   }
}

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Just an example.