# Exercise: Rename the Telemetry

Write two small tools for Mission Control, a script that renames every .tmp file in a folder and one that pulls the warnings out of a flight log, then run them on the real files and let a check script tell you what's done.

Apprentice · Unix · Linux · Updated November 10, 2026

It's launch day at Mission Control, and the ground station needs two small tools. The satellite's 21 telemetry files came in ending in `.tmp` instead of `.log`, and the flight director wants every warning from last night's flight log in one short report. You'll write both as scripts, small applications that work on whatever folder or file they're given, then run them on the real files. A check script tries each one on files of its own and tells you what's done.

## Before you start

You need a terminal: the Terminal app on a Mac, or Ubuntu on Linux or in WSL on Windows. The check runs with **bats**, a small program that runs checks written for bash. If `bats --version` doesn't print a version number yet, install it:

```bash
sudo apt install bats       # Ubuntu, and Ubuntu in WSL
brew install bats-core      # a Mac, with Homebrew
```

`sudo` asks for your password, the one you use to sign in; nothing shows on the screen while you type it.

## Get the exercise code

Open this lesson's GitHub repository, [github.com/ask-codey/exercise-bash-rename-the-telemetry](https://github.com/ask-codey/exercise-bash-rename-the-telemetry), also linked from the **Exercise** box beside the lesson. Click **Code**, then **Download ZIP**, and unzip it into your `terminal-practice` folder. Or clone it with Git. On Windows, put it inside Ubuntu, in your Linux home folder, not in a Windows folder under `/mnt/c`, so `chmod` works on the scripts.

The folder holds:

- `rename.sh` and `warnings.sh`: the two scripts. Each starts with a comment that says exactly what it must do. These are the files you write.
- `telemetry/`: the 21 telemetry files, all ending in `.tmp`. One has spaces in its name.
- `flight-log.txt`: last night's flight log, with notes from the night shift and a few lines after the end.
- `check.bats`: the check. You don't need to change it.

## What to do

Open a terminal in the exercise folder, make the scripts runnable (*Your First Script*), and open the first one in nano:

```bash
chmod +x rename.sh warnings.sh
nano rename.sh
```

1. **`rename.sh FOLDER`** renames every `.tmp` file in the folder it's given to end in `.log`, prints a line for each file it renames, and ends with `Files renamed: 21` (or however many it renamed). Run a second time, with nothing left to rename, it prints `Files renamed: 0` and no error.
2. **`warnings.sh LOGFILE`** reads the log one line at a time, skips the notes that start with `#`, stops at the line `END OF FLIGHT`, prints every other line with `WARNING` in it exactly as written, and ends with `Warnings found: 3` (or however many it printed).
3. **Use them.** Try `rename.sh` on a copy first (`cp -r telemetry practice`, then `./rename.sh practice`, then `rm -r practice`). When the checks for a script pass, run it on the real files:

   ```bash
   ./rename.sh telemetry
   ./warnings.sh flight-log.txt > warnings.txt
   ```

`rename.sh` uses a `for` loop and `warnings.sh` uses `while IFS= read -r line`, and each works on its `$1` (*Arguments: $1, $# and "$@"*), never on a name written into the script.

## Check your work

From the exercise folder:

```bash
bats check.bats
```

At first almost every check fails. That's expected: each job you finish turns its checks into a ✓. The check tries your scripts on made-up files of its own, in a throwaway folder, and only the last two checks look at your `telemetry/` folder and `warnings.txt`. A failing check says what to look at, for example *With four .tmp files, the last line should be: Files renamed: 4. Start a counter at 0 before the loop, add 1 for each file inside it, and print it after done.*

## Hints

- **The renaming line** is the one from *For Every File: for Loops*. In `for f in "$1"/*.tmp`, the double quotes go around `$1` only, so the `*` still matches.
- **Look before you rename:** put `echo` in front of `mv` and run the script on your `practice` copy.
- **The count** starts at 0 before the loop and grows inside it (*Stopping Early: break, continue and Counters*), and the same lesson shows the line that makes a loop safe to run twice.
- **Spaces and backslashes** in the log must come out as they went in: *Line by Line: while read* says which part of the loop keeps each, and `echo "$line"` needs its double quotes.
- **Inside `[[ ]]`**, `$line == "#"*` means "starts with #", and `$line == *WARNING*` means "has WARNING somewhere in it".

## When you're done

Every check passes:

```text
check.bats
 ✓ rename.sh and warnings.sh are here
 ✓ 1) rename.sh renames every .tmp file in the folder it's given
 ✓ 2) rename.sh prints how many files it renamed
 ✓ 3) rename.sh is safe to run twice
 ✓ 4) rename.sh uses a for loop
 ✓ 5) warnings.sh prints each warning exactly as written
 ✓ 6) warnings.sh skips the notes that start with #
 ✓ 7) warnings.sh stops at END OF FLIGHT
 ✓ 8) warnings.sh prints how many warnings it found
 ✓ 9) warnings.sh reads the log with while IFS= read -r
 ✓ 10) the telemetry folder is renamed
 ✓ 11) warnings.txt holds the flight log's warnings
12 tests, 0 failures
```

Now look back at `rename.sh`. It renames `.tmp` to `.log` and nothing else. What would you change so the same script could turn `.JPG` into `.jpg` in your photos folder, without writing a new one?

Want the whole mission? Play Mission Control from the start in Terminal Quest: [play it on the game's page](https://www.ask-codey.com/games/terminal-quest/mission-control/bash/step). It has the telemetry and the sensor check from this chapter, a beacon that takes an argument, and the launch itself. One goal stops a runaway program with `ps` and `kill`, which are new here; the Step by step hints show you how. The game keeps your place in this browser, so you can stop and come back.

## Submit your exercise

The exercise is how you finish this lesson. When your work is done, put it on GitHub in a repo of your own, then submit that repo's address here.

1. On GitHub, click **+**, then **New repository**. Name it (for example `exercise-bash-rename-the-telemetry`), choose **Public**, and click **Create repository**. Leave out the README: your folder already has one.
2. In a terminal in your exercise folder (Ubuntu in WSL on Windows), send your work to your new repo. If you downloaded the ZIP:

   ```bash
   git init -b main
   git add .
   git commit -m "My solution"
   git remote add origin https://github.com/your-name/exercise-bash-rename-the-telemetry.git
   git push -u origin main
   ```

   If you cloned the starter instead, point your copy at your own repo, then commit and push:

   ```bash
   git remote set-url origin https://github.com/your-name/exercise-bash-rename-the-telemetry.git
   git add .
   git commit -m "My solution"
   git push -u origin main
   ```

3. Paste your repo's address, such as `https://github.com/your-name/exercise-bash-rename-the-telemetry`, into **Submit your exercise** on this page. The site checks that the repo is public and holds your commits, and then the lesson is complete.

Changed something after you submitted? Push it, and submit again: your latest submission is the one that counts.

## So what

You wrote two tools that do in a second what would take an hour by hand, on 21 files or 2,000, and are safe to run again tomorrow: that is what a script that's an application looks like.

## Key terms

- [for Loop](https://www.ask-codey.com/glossary/for-loop-unix)
- [while Loop](https://www.ask-codey.com/glossary/while-loop-unix)
- [Parameter Expansion](https://www.ask-codey.com/glossary/parameter-expansion)
- [IFS](https://www.ask-codey.com/glossary/ifs)
- [continue](https://www.ask-codey.com/glossary/continue-unix)
- [break](https://www.ask-codey.com/glossary/break-unix)

## Related

- [For Every File: for Loops](https://www.ask-codey.com/lessons/bash-for-loops)
- [Line by Line: while read](https://www.ask-codey.com/lessons/bash-while-read)
- [Stopping Early: break, continue and Counters](https://www.ask-codey.com/lessons/bash-loop-control)

Source: https://www.ask-codey.com/lessons/exercise-bash-rename-the-telemetry