> For the complete documentation index, see [llms.txt](https://42-guide.gitbook.io/42-guide/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://42-guide.gitbook.io/42-guide/piscine-life/shell01/print_groups.md).

# print\_groups

**Objective:**

Write a shell script named `print_groups.sh` that displays the list of groups for which the user (stored in the environment variable `FT_USER`) is a member. The output should be a **comma-separated list of group names**, without spaces or newlines.

***

**Key Concepts:**

1. **Environment Variables**: These are variables that are set in the shell and can be accessed by scripts. In this case, `FT_USER` is an environment variable that contains the username.
2. **`id` Command**: The `id` command is used to display user and group information for a specified user. It can show the groups a user belongs to.
3. **Text Manipulation**: You will need to manipulate the output of the `id` command to format it as a comma-separated list without spaces or newlines.

***

**Script Implementation:**

Here’s the script you will use:

```bash
#!/bin/sh
id -Gn $FT_USER | tr ' ' ',' | tr -d '\n'
```

***

**Explanation of the Script:**

Let’s break down the script line by line:

1. **`#!/bin/sh`**:
   * This is called a **shebang**. It tells the system that this script should be executed using the `/bin/sh` shell, which is a basic shell available on most Unix-like systems.
2. **`id -Gn $FT_USER`**:

   * The `id` command is used to retrieve user and group information.
   * The `-Gn` options do the following:
     * `-G`: Lists all the groups the user belongs to.
     * `-n`: Displays the group names instead of their numeric IDs.
   * `$FT_USER` is the environment variable that contains the username. The script uses this variable to get the group information for the specified user.

   **Example**: If `FT_USER=daemon`, the output of `id -Gn $FT_USER` might look like this:

   ```
   daemon bin
   ```
3. **`tr ' ' ','`**:

   * The `tr` command is used to **translate or replace characters**.
   * In this case, it replaces all spaces ( ) with commas (`,`).
   * After this step, the output from the previous command (`daemon bin`) becomes

   ```
   daemon,bin
   ```
4. **`tr -d '\n'`**:

   * The `tr -d` command is used to **delete specific characters**.
   * Here, it removes the newline character () from the output.
   * This ensures that the final output is a single line without any newlines.

   **Final Output**:

   ```
   daemon,bin
   ```

***

**Testing the Script:**

To test your script, follow these steps:

1. **Set the Environment Variable**:
   * First, set the `FT_USER` environment variable to a valid username on your system. For example:

     ```bash
     export FT_USER=daemon
     ```
2. **Run the Script**:
   * Execute the script:

     ```
     ./print_groups.sh
     ```
3. **Expected Output**:
   * If `FT_USER=daemon`, the output should be:

     ```
     daemon,bin
     ```

***

**Why This Script Works:**

* The `id -Gn` command retrieves the list of groups for the user.
* The `tr ' ' ','` command replaces spaces with commas to create a comma-separated list.
* The `tr -d '\n'` command removes any newline characters, ensuring the output is clean and on a single line.

***

**Additional Resources:**

* **`id` Command Documentation**: Learn more about the `id` command by typing `man id` in your terminal or visiting the [GNU Coreutils documentation](https://www.gnu.org/software/coreutils/manual/coreutils.html#id-invocation).
* **Environment Variables**: For more information on environment variables, check out this [guide on environment variables](https://linuxize.com/post/how-to-set-and-list-environment-variables-in-linux/).
* **`tr` Command Documentation**: Learn more about the `tr` command by typing `man tr` or visiting the [GNU Coreutils documentation](https://www.gnu.org/software/coreutils/manual/coreutils.html#tr-invocation).

***

**Key Takeaways:**

* You learned how to use the `id` command to retrieve group information for a user.
* You practiced using the `tr` command to manipulate text output (replacing spaces with commas and removing newlines).
* You worked with environment variables to make your script dynamic and reusable.

This exercise is a great introduction to shell scripting and text manipulation. Keep practicing, and you'll get more comfortable with these concepts!


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