/tmp>echo 'echo Hello from the shell' > demo
/tmp>chmod +x demo
/tmp>./demo
Hello from the shell
/tmp>echo '#!/no/such/exe' > demo
/tmp>echo 'echo Hello from the shell' >> demo
/tmp>chmod +x demo
/tmp>./demo
-bash: ./demo: /no/such/exe: bad interpreter: No such file or directory
/tmp>chmod -x demo
/tmp>./demo
-bash: ./demo: Permission denied
/tmp>