Week 1 Homework - Shell Scripting

Time estimate: 1.5 hours maximum

Submission: Create a directory week1-[netid] with your solutions and add it as a submodule to the class repo.

Note

Make sure you check out week1 installation instructions before starting this homework.

Setup

Create your homework directory:

mkdir week1-[netid]
cd week1-[netid]

All scripts should be executable (chmod +x script.sh) and include a proper shebang (#!/usr/bin/env bash).

Exercise 1: Custom `ls` (15 minutes)

Read man ls and write an ls command that lists files with the following properties:

Includes all files, including hidden files
Sizes are in human-readable format (e.g., 454M instead of 454279954)
Files are ordered by recency (most recently modified first)
Output is colorized

Save your command in a file called ex1_command.txt.

Sample output:

-rw-r--r--   1 user group 1.1M Jan 14 09:53 baz
drwxr-xr-x   5 user group  160 Jan 14 09:53 .
-rw-r--r--   1 user group  514 Jan 14 06:42 bar
-rw-r--r--   1 user group 106M Jan 13 12:12 foo
drwx------+ 47 user group 1.5K Jan 12 18:08 ..

Hint: Look for flags related to “all”, “human-readable”, “time”, and “color” in the man page.

Exercise 2: Semester Setup Script (20 minutes)

Write a bash script called semester that creates a directory structure for organizing coursework.

Requirements:

The script should:

Take a semester name as an argument (e.g., fall2025)

Create the following directory structure:

fall2025/
├── comp140/
├── comp182/
├── math212/
└── projects/

Create a README.md file in the root directory with:
- The semester name
- The current date (use date)
- A placeholder for course descriptions

Example usage:

./semester fall2025

Expected output:

Created semester directory: fall2025
Created course directories: comp140, comp182, math212, projects
Created README.md

Bonus: Make the course names configurable via additional arguments.

Exercise 3: `marco` and `polo` (20 minutes)

Write two bash functions that work together for directory navigation:

marco - Saves the current working directory
polo - Returns you to the directory where you last executed marco

Requirements:

Create a file called navigation.sh
Implement both functions
The saved directory should persist across terminal sessions (hint: save to a file)
If polo is called before marco, print a helpful error message

Example usage:

$ source navigation.sh
$ cd /usr/local/bin
$ marco
Saved current directory
$ cd ~
$ cd Documents
$ pwd
/home/user/Documents
$ polo
$ pwd
/usr/local/bin

Hint: You’ll need to save the directory to a file in your home directory (like ~/.marco_location).

Exercise 4: Retry Script (25 minutes)

Write a bash script called retry.sh that runs a command until it fails, then reports statistics.

The script should:

Take another script as an argument
Run it repeatedly until it exits with a non-zero status
Capture both stdout and stderr to separate files
Report:
- Number of successful runs before failure
- The final error message
- Total time elapsed

Test it with this script (save as flaky.sh):

#!/usr/bin/env bash

n=$(( RANDOM % 100 ))

if [[ $n -eq 42 ]]; then
   echo "Something went wrong"
   >&2 echo "The error was using magic numbers"
   exit 1
fi

echo "Everything went according to plan"

Example usage:

$ ./retry.sh ./flaky.sh
Run 1: success
Run 2: success
Run 3: success
...
Run 47: FAILED

Statistics:
- Successful runs: 46
- Failed on run: 47
- Total time: 2.3 seconds

Error output:
The error was using magic numbers

Standard output from failed run:
Something went wrong

Hints:

Use a while loop with a counter
Check $? after each run
Use date +%s to track time
Redirect output: command > stdout.log 2> stderr.log

Exercise 5: HTML Archive Creator (20 minutes)

Write a command (can be a one-liner or script called archive_html.sh) that:

Recursively finds all HTML files in the current directory
Creates a tar.gz archive containing them
Handles filenames with spaces correctly
Names the archive with today’s date: html_backup_YYYY-MM-DD.tar.gz

Requirements:

Must work even if files have spaces in their names
Should use find combined with xargs or find -exec
Should create the archive in the current directory

Test setup:

mkdir -p test/web/{pages,styles}
touch test/web/index.html
touch test/web/pages/"about us.html"
touch test/web/pages/contact.html
touch test/web/styles/main.css

Expected result:

$ ./archive_html.sh
Found 3 HTML files
Created archive: html_backup_2025-01-20.tar.gz

Hints:

find . -name "*.html" finds HTML files
Use find -print0 with xargs -0 for handling spaces
Or use find -exec tar ...
Use date +%Y-%m-%d for the date format

Exercise 6: Log Analyzer (20 minutes)

Write a script called analyze_logs.sh that processes a log file and produces a summary report.

Given this sample log file (save as server.log):

2025-01-20 10:23:15 INFO Server started on port 8080
2025-01-20 10:23:18 INFO Connected to database
2025-01-20 10:24:32 WARNING High memory usage: 85%
2025-01-20 10:25:01 ERROR Failed to connect to redis
2025-01-20 10:25:15 INFO User login: alice@rice.edu
2025-01-20 10:26:42 ERROR Database timeout
2025-01-20 10:27:03 INFO User login: bob@rice.edu
2025-01-20 10:28:15 WARNING Disk space low: 5% remaining
2025-01-20 10:29:01 ERROR Connection refused
2025-01-20 10:30:12 INFO User login: charlie@rice.edu

Your script should output:

$ ./analyze_logs.sh server.log

Log Analysis Report
===================
Total lines: 10
INFO messages: 5
WARNING messages: 2
ERROR messages: 3

Most recent error:
2025-01-20 10:29:01 ERROR Connection refused

Unique users logged in: 3

Requirements:

Use grep, wc, and other text processing tools
Extract and count different log levels
Find the most recent error
Count unique user logins

Hints:

grep -c "pattern" counts matches
tail -1 gets the last line
Use cut or awk to extract specific fields
sort | uniq | wc -l counts unique values

Exercise 7 (Bonus/Advanced): Recent File Finder (10 minutes)

Write a script or one-liner that finds and lists the most recently modified files in a directory tree.

Requirements:

Recursively search from current directory
Find the 10 most recently modified files
Display: modification time, file size (human-readable), and file path
Exclude hidden files and directories

Example output:

$ ./recent_files.sh
Jan 20 14:32  1.2M  ./reports/analysis.pdf
Jan 20 14:15  456K  ./data/results.csv
Jan 20 13:58   12K  ./scripts/process.py
...

Hints:

Use find with -type f and -mtime
Combine with ls -lht or use find -printf
Use head to limit results
May need to exclude paths matching */.*

Submission Checklist

Your week1-[netid] directory should contain:

week1-netid/
├── ex1_command.txt
├── semester
├── navigation.sh
├── retry.sh
├── flaky.sh (provided)
├── archive_html.sh
├── analyze_logs.sh
├── server.log (provided)
└── recent_files.sh (bonus)

Before submitting:

Make all scripts executable: chmod +x *.sh semester
Test each script works as described
Add comments explaining tricky parts
Run shellcheck if available: shellcheck *.sh

Submit by: Adding your directory as a git submodule and pushing to your repo

Grading

Exercises 1-4: Required (90%)
Exercises 5-6: Required (10%)
Exercise 7: Bonus (5% extra credit)

Remember: If any exercise takes more than the estimated time, stop and ask for help in office hours. The goal is learning, not frustration!

Tips

Test incrementally - don’t write the whole script at once
Use echo statements to debug
Check exit codes: echo $?
Quote your variables: "$var" not $var
Read error messages carefully
Use shellcheck to catch common mistakes

Good luck, and remember: the best programmers are lazy programmers who automate everything!

The Art Of Lazy Programming