[module]
name = "ls"
description = "List directory contents — navigate the filesystem and audit file state"
version = 1
[intro]
text = """
## Why ls matters
`ls` is almost always the first command you run in an unfamiliar directory. When you SSH into a server, clone a repo, or land in a production container, `ls` is how you orient yourself: what files exist, how they're named, whether config files are present, whether logs have accumulated.
In day-to-day engineering work `ls` does more than just list names. With the right flags you can:
- Spot whether `.env` or other secret files are accidentally present before a commit
- Check timestamps after a `git pull` to see which files actually changed
- Find the largest files eating disk space on a server
- Confirm that a deployment wrote the expected output files
- Understand a project's structure at a glance before opening any file
Because `ls` output goes to stdout it composes naturally with pipelines: `ls | wc -l` counts files, `ls *.log | xargs rm` bulk-deletes logs, `ls -t | head -1` finds the most recently modified file.
## Key flags
- `-l` — long format: shows permissions, owner, group, size (bytes), modification date, and name. Essential for auditing who owns a file and whether it's executable.
- `-a` — show **all** entries including `.` (current dir) and `..` (parent dir) and all dotfiles.
- `-A` — like `-a` but omits `.` and `..`. Almost always what you want when you need hidden files.
- `-h` — human-readable sizes when combined with `-l`: prints `4.2M` instead of `4194304`.
- `-t` — sort by modification time, newest first. Pair with `head` to find the most recently touched file after a deployment or `git pull`.
- `-S` — sort by file size, largest first. Useful for finding what's eating disk space.
- `-r` — reverse the sort order. Combined with `-t` gives oldest-first; combined with `-S` gives smallest-first.
- Flag combinations: `ls -lhS` (long, human-readable, by size), `ls -ltr` (long, by time, oldest first — good for reading a deployment sequence).
## Real-world workflows
**After a git pull — see what actually changed:**
```
ls -lt | head -20
```
Sorts by modification time so the files touched by the pull appear at the top.
**Checking for accidentally committed secrets:**
```
ls -A | grep -E '^\\.env'
```
Lists hidden files and filters for `.env` variants before you push to a public repo.
**Disk auditing on a server:**
```
ls -lhS /var/log | head -10
```
Shows the ten largest log files in `/var/log` with human-readable sizes so you know what to rotate or delete.
"""
[[examples]]
title = "List files in current directory"
description = "Show all non-hidden files in the working directory, one per line"
command = "ls"
output = "README.md\napp.py\nconfig.yaml\nmain.py\n"
[[examples]]
title = "Show hidden dotfiles"
description = "List all files including dotfiles, but exclude . and .."
command = "ls -A"
output = ".env\n.gitignore\napp.py\n"
[[exercises]]
id = "ls.1"
difficulty = "beginner"
question = """List the files in the current project directory."""
expected_output = "README.md\napp.py\nconfig.yaml\nmain.py\n"
hints = [
"ls lists the current directory by default",
"Try: ls",
]
solution = "ls"
match_mode = "exact"
[[exercises.fixtures]]
filename = "README.md"
content = "# placeholder\n"
[[exercises.fixtures]]
filename = "app.py"
content = "# placeholder\n"
[[exercises.fixtures]]
filename = "config.yaml"
content = "# placeholder\n"
[[exercises.fixtures]]
filename = "main.py"
content = "# placeholder\n"
[[exercises]]
id = "ls.2"
difficulty = "beginner"
question = """The project directory contains regular files and hidden dotfiles (files starting with `.`). List ALL files including hidden ones, but exclude `.` and `..`."""
expected_output = ".env\n.gitignore\napp.py\n"
hints = [
"Regular ls hides files whose names start with a dot",
"The -A flag shows hidden files but skips . and ..",
"Try: ls -A",
]
solution = "ls -A"
match_mode = "exact"
[[exercises.fixtures]]
filename = "app.py"
content = "# placeholder\n"
[[exercises.fixtures]]
filename = ".env"
content = "DATABASE_URL=localhost\n"
[[exercises.fixtures]]
filename = ".gitignore"
content = "*.pyc\n__pycache__/\n"
[[exercises]]
id = "ls.3"
difficulty = "beginner"
question = """The directory contains Python source files alongside configuration and dependency files. List only the Python (`.py`) files."""
expected_output = "auth.py\nmain.py\nutils.py\n"
hints = [
"ls accepts glob patterns to filter by extension",
"Try: ls *.py",
]
solution = "ls *.py"
match_mode = "exact"
[[exercises.fixtures]]
filename = "auth.py"
content = "# placeholder\n"
[[exercises.fixtures]]
filename = "main.py"
content = "# placeholder\n"
[[exercises.fixtures]]
filename = "config.yaml"
content = "# placeholder\n"
[[exercises.fixtures]]
filename = "requirements.txt"
content = "# placeholder\n"
[[exercises.fixtures]]
filename = "utils.py"
content = "# placeholder\n"
[[exercises]]
id = "ls.4"
difficulty = "intermediate"
question = """Count how many files are in the current directory. Print just the number."""
expected_output = "5\n"
hints = [
"Pipe ls output into wc -l to count lines",
"BSD wc adds leading spaces — strip them with tr -d ' '",
"Try: ls | wc -l | tr -d ' '",
]
solution = "ls | wc -l | tr -d ' '"
match_mode = "normalized"
[[exercises.fixtures]]
filename = "file1.txt"
content = "data\n"
[[exercises.fixtures]]
filename = "file2.txt"
content = "data\n"
[[exercises.fixtures]]
filename = "file3.txt"
content = "data\n"
[[exercises.fixtures]]
filename = "file4.txt"
content = "data\n"
[[exercises.fixtures]]
filename = "file5.txt"
content = "data\n"
[[exercises]]
id = "ls.5"
difficulty = "intermediate"
question = """List the files in the current directory in reverse alphabetical order (Z → A)."""
expected_output = "gamma.txt\ndelta.txt\nbeta.txt\nalpha.txt\n"
hints = [
"ls outputs in alphabetical order by default",
"Pipe through sort -r to reverse the order",
"Try: ls | sort -r",
]
solution = "ls | sort -r"
match_mode = "exact"
[[exercises.fixtures]]
filename = "alpha.txt"
content = "# placeholder\n"
[[exercises.fixtures]]
filename = "beta.txt"
content = "# placeholder\n"
[[exercises.fixtures]]
filename = "gamma.txt"
content = "# placeholder\n"
[[exercises.fixtures]]
filename = "delta.txt"
content = "# placeholder\n"
[[exercises]]
id = "ls.6"
difficulty = "advanced"
question = """You're checking test coverage for a project. Count the number of test files (files whose names start with `test_` and end in `.py`)."""
expected_output = "3\n"
hints = [
"Use a glob pattern to match files starting with test_ and ending in .py",
"Pipe the result to wc -l and strip leading spaces with tr -d ' '",
"Try: ls test_*.py | wc -l | tr -d ' '",
]
solution = "ls test_*.py | wc -l | tr -d ' '"
match_mode = "normalized"
[[exercises.fixtures]]
filename = "test_auth.py"
content = "# placeholder\n"
[[exercises.fixtures]]
filename = "test_api.py"
content = "# placeholder\n"
[[exercises.fixtures]]
filename = "test_db.py"
content = "# placeholder\n"
[[exercises.fixtures]]
filename = "auth.py"
content = "# placeholder\n"
[[exercises.fixtures]]
filename = "api.py"
content = "# placeholder\n"
[[exercises.fixtures]]
filename = "conftest.py"
content = "# placeholder\n"