Why does behavior of `./example` and `sh example` different? (`zsh: text file busy: ./example`)

Question

I tried this:

$ exec 3> example
$ lsof example 
COMMAND   PID USER   FD   TYPE DEVICE SIZE/OFF    NODE NAME
zsh     10711 lane    3w   REG  253,0        0 9231034 example

It will show text file busy if I do this:

$ ./example  
zsh: text file busy: ./example

But if I execute it using sh, it will be OK(no error):

$ sh example 
$

What is the difference between ./example and sh example?

Answer 1

When you do

$ ./example

you are trying to execute "example" which is being written to. This is not allowed.

When you do

$ sh example

sh is reading "example", then execute what is read. This is fine.

Answer 2

There are different shell environments on the Linux, such as sh, bash, zsh and etc. In some shells, there are differences in the execution of the bash script. when you use ./example it execute the script in the current shell. when you use with bash example or sh example it will run on the the specific shell you want. also you can use shebang in the first line of you script.