grep1-2  Exercise 3: Passwords, Hidden Files and a Name with Spaces
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(Run from an empty folder. The first block builds the practice project from the chapter; your own tree can skip it.)

mkdir -p project/src project/notes project/build project/logs project/data project/.git "project/my notes"
cd project

printf '# Demo project\nTODO write the install guide\nRun app.py to start\n' > README.md
printf 'import os\n# TODO handle errors\ndef main():\n    print("hello")\n' > app.py
printf 'def helper():\n    # TODO remove this\n    return 1\n' > src/util.py
printf '// TODO rename\nconsole.log("hi");\n' > src/main.js
printf 'buy milk\nTODO call the plumber\n' > notes/todo.txt
printf '/* generated */ var a = 1; // TODO generated noise\n' > build/bundle.js
printf 'INFO started\nERROR something broke\n' > logs/app.log
printf 'data\0TODO inside a binary file\n' > data/image.bin
printf 'API_KEY=abc123\npassword=hunter2\n' > .env
printf '[core]\n\trepositoryformatversion = 0\n# TODO placeholder inside .git\n' > .git/config
printf 'TODO book the room\npassword reminder: change it\n' > "my notes/meeting notes.txt"

# --- the exercise ---
echo "--- by listing with a star: misses hidden files"
grep -rl password *
echo "--- walking the folder: finds .env too"
grep -rl password .
echo "--- the version that breaks on a space:"
grep -rl password . | xargs wc -l
echo "--- the safe version:"
grep -rlZ password . | xargs -0 wc -l

Output:

--- by listing with a star: misses hidden files
my notes/meeting notes.txt
--- walking the folder: finds .env too
./.env
./my notes/meeting notes.txt
--- the version that breaks on a space:
 2 ./.env
wc: ./my: No such file or directory
wc: notes/meeting: No such file or directory
wc: notes.txt: No such file or directory
 2 total
--- the safe version:
 2 ./.env
 2 ./my notes/meeting notes.txt
 4 total

WHY THIS WORKS AS AN ANSWER
---------------------------
The star version misses .env because the shell never passes names that start with a dot. The dot version lets grep walk the folder itself.
In the broken version xargs splits './my notes/meeting notes.txt' at the spaces, so wc is asked about './my', 'notes/meeting' and 'notes.txt', none of which exist, and it reports an error for each while still counting the file it could read.
In the safe version -Z ends each name with a zero byte and xargs -0 splits on that, so the name arrives as one argument. The total line is wc's own.