# Your First Script

A script is a file of commands that starts with the shebang line #!/usr/bin/env bash and explains itself in comments; chmod +x lets it run, and ./ and its name runs it from the folder it's in.

Apprentice · Unix · Linux · Updated November 10, 2026

## After this lesson you can

- Write a script file that starts with a shebang line naming bash, and explains itself in comments
- Make a script runnable with chmod +x and run it with ./ from its folder, or with bash and its name

## Key takeaways

- A script is a text file of commands, run top to bottom. The name ending .sh tells people and editors it's a shell script.
- The first line, #!/usr/bin/env bash, read "shebang", says which program runs the file. It must be the very first line.
- A line starting with # is a comment, a note for people that bash skips.
- A new file may not run. chmod +x morning.sh lets it run, and ./morning.sh runs it from the folder it's in.
- bash morning.sh runs a script without the x permission, which is handy for a quick try.

Every morning this week you've opened a terminal and typed the same commands: a greeting to yourself, `date`, `cat` on your to-do list, and `df -h` to check the disk isn't filling up. Four commands is a small thing, but it's every single day, and on the busy mornings you skip the disk check and forget it for a month. Put the commands in a file, and one word does them all, in order, every time. That file is your first script, and it's how every automation people get paid for starts.

Make a practice folder with a to-do list in it. These lines are safe to run again:

```bash
mkdir -p ~/terminal-practice/morning && cd ~/terminal-practice/morning
printf 'pay the phone bill\nfinish the history essay\nbuy coffee beans\n' > todo.txt
```

## A file of commands

Open a new file in nano (*Editing in the Terminal: nano*) with `nano morning.sh`, and type these lines:

```bash
#!/usr/bin/env bash
# morning.sh: my start-of-the-day check.
# Greets me, then shows the date, my to-do list and the free disk space.

echo "Good morning, $USER!"
date '+Today is %A, %B %d.'

echo
echo "To do:"
cat todo.txt

echo
echo "Free disk space:"
df -h ~
```

Save with **Ctrl+O** and Enter, and quit with **Ctrl+X**. Every line below the first three is a command you could type at the prompt. `$USER` is the environment variable that holds your user name (*Environment Variables: export and env*). `date` with a `+` and a pattern prints the date your way: `%A` is the day's name, `%B` the month's and `%d` the day's number. `echo` on its own prints an empty line, to space the output out.

A script runs its lines from top to bottom, the way a cook follows a recipe. The name ending `.sh` is a habit, not a rule: it tells people and editors that this is a shell script.

## The first line: #!/usr/bin/env bash

The first line tells the computer which program should run the file. It starts with `#!`, read "hash bang" and usually shortened to **shebang**. After it comes the program: `/usr/bin/env bash` means "find bash in the folders on my `PATH`, and run this file with it".

Why not write `#!/bin/bash`? On Linux it would work. But a Mac's `/bin/bash` is version 3.2, from 2006, and the bash 5 you installed with Homebrew lives in a different folder. `env` finds whichever bash comes first on your `PATH`, so the same script runs on both. The shebang must be the very first line, with nothing before it, not even a blank line.

## Comments: notes for people

Lines two and three start with `#` (read "hash"). That makes them **comments**: notes for people, which bash skips. The shebang looks like a comment too, and for bash it is one; only the computer, when it starts the file, reads it.

Write at least one comment at the top of every script: what it does, and anything future you would want to know. In three months, `# Greets me, then shows the date, my to-do list and the free disk space.` saves you reading every line. A comment can also go at the end of a command, after a space: `df -h ~   # the drive my home folder is on`.

## chmod +x, then ./ and its name

Run it the way you ran the kettle-bot in *Permissions: Read, Write and Run*: `./` (read "dot slash": this folder, this file) and its name.

```bash
./morning.sh
ls -l morning.sh
```

```text
bash: ./morning.sh: Permission denied
-rw-r--r-- 1 sam sam 262 Nov  9 06:08 morning.sh
```

A new file can be read and changed, but there's no `x` in its permissions, so it may not run. `chmod +x` adds it, once:

```bash
chmod +x morning.sh
./morning.sh
```

```text
Good morning, sam!
Today is Monday, November 09.

To do:
pay the phone bill
finish the history essay
buy coffee beans

Free disk space:
Filesystem      Size  Used Avail Use% Mounted on
/dev/sdd       1007G   30G  926G   4% /
```

That's your first application, running. Yours shows your name, today's date and your own disk. On a Mac, the disk line names a different drive.

There's a second way to run a script: hand it to bash yourself, with `bash morning.sh`. Bash reads the file, so it needs only read permission, not `x`. It's handy for a quick try, but a script you'll keep should get `chmod +x` and its shebang, so it runs like any other program.

## Try it in the terminal

[Terminal Quest: Mission Control, goal 1](https://www.ask-codey.com/games/terminal-quest/mission-control/bash/step): played right on the lesson page.

Launch day at Mission Control, and the flight director wants scripts, not clicks. Read her briefing: it lists the jobs your scripts will do, and how to write the first one.

## Check yourself

2 questions to try on the lesson page.

## So what

A shebang, a comment, a few commands and `chmod +x`: that's a whole application. Every script you write from now on, however big, starts exactly like this one.

## Key terms

- [Shell Script](https://www.ask-codey.com/glossary/shell-script)
- [Shebang](https://www.ask-codey.com/glossary/shebang)
- [Comment](https://www.ask-codey.com/glossary/comment-unix)
- [chmod](https://www.ask-codey.com/glossary/chmod)
- [File Permissions](https://www.ask-codey.com/glossary/file-permissions)

## Cheat sheets

- [Your First Script](https://www.ask-codey.com/cheat-sheets/bash-your-first-script-cheat-sheet)

## Related

- [A Script Is an Application](https://www.ask-codey.com/lessons/bash-scripts-are-applications)
- [Editing in the Terminal: nano](https://www.ask-codey.com/lessons/bash-editing-with-nano)
- [Permissions: Read, Write and Run](https://www.ask-codey.com/lessons/bash-permissions)
- [Run It from Anywhere: ~/bin on Your PATH](https://www.ask-codey.com/lessons/bash-scripts-on-your-path)

Source: https://www.ask-codey.com/lessons/bash-your-first-script