```
$ touch script.sh

$ atom script.sh

$ sh script.sh
Hello, world!

$ ./script.sh
zsh: permission denied: ./script.sh

$ type chmod
chmod is /bin/chmod

$ ls -l script.sh
-rw-r--r--  1 bc  staff  21 23 Aug 15:56 script.sh

$ chmod 700 script.sh

$ ls -l script.sh
-rwx------  1 bc  staff  21 23 Aug 15:56 script.sh

$ ./script.sh
Hello, world!

$ chmod +x script.sh

$ ls -l script.sh
-rwx--x--x  1 bc  staff  21 23 Aug 15:56 script.sh

$ ./script.sh
Hello, world!
```