Difference between "echo 'hello'; ls" vs "echo 'hello' && ls"?

Question

I wonder what the difference between

"echo 'hello'; ls"

and

"echo 'hello' && ls"

is? they both do the same thing

Answer 1

"echo 'hello' && ls" means : execute "ls" if "echo 'hello'" runs successfully. To understand what is "successful" in bash. Try this :

bash> cd /
bash> echo $?

if the previous command runs successfully, you should see 0

After that, try this :

bash> asdfdf
bash> echo $?

You should see a non-zero value between 1 and 255. This means previous command didn't run successfully

On the other hand, "echo 'hello'; ls" means execute "ls" whether "echo 'hello'" runs successfully or not.