Create an executable script

A shell script is a text file containing commands. When you run it, the operating system starts an interpreter and feeds it the file. The interpreter line on the first line — often called the shebang — tells the operating system which program should read it.

Write the script

Create a file named hello:

#!/usr/bin/env bash

printf '%s\n' 'hello from a script'

The first line must start with #!. I use #!/usr/bin/env bash instead of a hardcoded /bin/bash because env finds Bash wherever it lives on PATH. On macOS the system Bash in /bin is ancient, and the current one from Homebrew sits somewhere else entirely. env picks the right one on each machine.

printf '%s\n' 'text' is the predictable way to print. Unlike echo, it never reinterprets escapes or flags hidden inside the value.

Make it executable and run it

A fresh file is not executable. Give yourself execute permission, then run it:

chmod u+x hello
./hello
# hello from a script

If you skip chmod, the shell answers Permission denied. That error means the file exists but you’re not allowed to execute it — the fix is the permission, not the path.

Why the ./ prefix

The ./ prefix names the file in the current directory. Without a slash, the shell searches directories in PATH, and the current directory is not on that list:

hello
# bash: hello: command not found
./hello
# hello from a script

This trips up everyone once. command not found for a file sitting right there means you forgot the ./.

Do not add the current directory to PATH globally to “fix” this. Any directory you cd into could then shadow real commands with a malicious file named ls. Run local scripts through an explicit path.

The shebang stays in charge

You can also run a script without execute permission by naming the interpreter yourself:

bash hello
# hello from a script

That works, but it ignores the shebang. If someone runs a Bash-only script with sh this way, the syntax breaks in confusing places. Making the file executable and running ./hello keeps the interpreter line in control.