How do I shoot bullet only once?

How do i shoot only once?

Example:

Touch to shoot a bullet and can't shoot more.

if this bullet overlaps another object => can shoot another bullet.

Please help me, sorry for my English

Many different ways

on touch start

bullet is not overlapping object- shoot bullet

on touch end

bullet is not overlapping object- shoot bullet

is touching

bullet is not overlapping object

system trigger once - shoot bullet

Oh, thank you. I do it. Amazing

From what I understand you want to have only one bullet, but you get another bullet if your first bullet hits a certain object?

If so, this should work with variables.

On touch, if variable =1

-shoot bullet

-set variable to 0

Bullet collide with object

-set variable to 1