> For the complete documentation index, see [llms.txt](https://gitbook.hbcomputersecurity.co.uk/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://gitbook.hbcomputersecurity.co.uk/core-technical-skills/core-skills/linux/shell-scripting/variables/command-substitution.md).

# Command Substitution

We can use command substitution so that a variable **contains the output of a command**, which would normally be output to the screen:

{% code title="Command Substitution" %}

```bash
user=$(whoami)
echo $user
Bob
```

{% endcode %}

This may look familiar to anyone who has been reading through this aide memoire - remember the section where we created [temporary user accounts](/core-technical-skills/core-skills/linux/system-administration/account-administration/standard-user-accounts.md#creating-temporary-user-accounts)? We were able to calculate 30 days in advance of the current date with command substitution.

You are only limited by your imagination - rather than list out tonnes of boring examples, have a play yourself and see what results you get within your variables