Command library.

Prints your current folder.

Run from ~/linux-practice

pwd

Shows the kernel, architecture, distribution details, and (when applicable) the WSL distribution name. These checks are safe on Ubuntu, most Linux distributions, and WSL.

Run from anywhere

uname -srmo
cat /etc/os-release
if [ -n "$WSL_DISTRO_NAME" ]; then echo "WSL distro: $WSL_DISTRO_NAME"; fi

Shows files in normal, detailed, hidden, human-readable, and time-sorted views.

Run from ~/linux-practice

ls
ls -l
ls -la
ls -lh
ls -ltr

Creates harmless files and a folder inside the sandbox.

Run from ~/linux-practice

touch file1.txt file2.txt file3.txt
mkdir testdir
ls -la

Moves home, then returns to the sandbox.

Run from ~/linux-practice

cd ~
pwd
cd ~/linux-practice
pwd

Shows how .. climbs up one level at a time.

Run from ~/linux-practice

cd ~/linux-practice
mkdir -p files/demo
cd files/demo
pwd
cd ..
pwd
cd ../..
pwd

cd - switches back to the last directory you were in, without retyping the path.

Run from ~/linux-practice

cd ~/linux-practice
cd /tmp
pwd
cd -
pwd

Visits Ubuntu configuration folders without editing anything.

Run from anywhere

cd /etc
pwd
ls -l | head -20
cd ~/linux-practice

Creates empty files and demonstrates brace expansion.

Run from ~/linux-practice

cd ~/linux-practice
touch myfile.txt
touch file_{1..5}.txt
ls -l

mkdir -p creates missing parent folders without failing when they already exist. rmdir removes only an empty directory, making it a safer first removal command than rm -r.

Run from ~/linux-practice

cd ~/linux-practice
mkdir -p files/{inbox,archive}
ls -ld files files/inbox files/archive
rmdir files/archive

Shows size, permissions, owner, timestamps, and inode.

Run from ~/linux-practice

stat myfile.txt

Compares a text file with a real executable.

Run from ~/linux-practice

echo 'Hello Ubuntu' > myfile.txt
file myfile.txt
file /bin/bash

Creates a file and appends another line. Remember: > overwrites.

Run from ~/linux-practice

cd ~/linux-practice
echo 'First line' > journal.txt
echo 'Second line' >> journal.txt
cat journal.txt

Shows numbered lines and reverse order.

Run from ~/linux-practice

cat -n journal.txt
tac journal.txt

Saves a directory listing while also displaying it.

Run from ~/linux-practice

ls -la | tee listing.txt
cat listing.txt

Generates a harmless file for viewing practice.

Run from ~/linux-practice

cd ~/linux-practice
for i in {1..100}; do echo "This is line number $i"; done > large.txt

Shows first lines, last lines, and counts.

Run from ~/linux-practice

head -n 5 large.txt
tail -n 5 large.txt
wc large.txt
wc -l large.txt

Press Space for next page, /pattern to search, and q to quit.

Run from ~/linux-practice

less -N large.txt

Demonstrates the difference between replace and append.

Run from ~/linux-practice

cd ~/linux-practice
echo 'First' > output.txt
echo 'Second' >> output.txt
cat output.txt

Sends stderr to a file instead of the screen.

Run from ~/linux-practice

ls missing-file 2> error.log
cat error.log

Creates multi-line text safely.

Run from ~/linux-practice

cat << 'EOF' > document.txt
Line 1
Line 2
Variables like $HOME are not expanded here
EOF
cat document.txt

Sorts lines and counts adjacent duplicates after sorting.

Run from ~/linux-practice

cd ~/linux-practice
echo -e 'banana\napple\ncherry\napple' > fruits.txt
sort fruits.txt | uniq -c

Transforms text through a pipeline.

Run from ~/linux-practice

echo 'Hello World' | tr 'a-z' 'A-Z'
echo 'Hello World' | tr ' ' '_'

Extracts fields and prints a simple table.

Run from ~/linux-practice

echo 'Name:Age:City' > people.txt
echo 'Jane:25:London' >> people.txt
cut -d: -f1,3 people.txt
column -t -s: people.txt

Finds matching and non-matching lines.

Run from ~/linux-practice

cd ~/linux-practice
echo -e 'Apple\napple\nAPPLE\nBanana\napricot' > fruits.txt
grep -i 'apple' fruits.txt
grep -v 'apple' fruits.txt

Uses start, end, and OR matching.

Run from ~/linux-practice

grep '^A' fruits.txt
grep 'e$' fruits.txt
grep -E 'apple|Banana' fruits.txt

Searches through folders.

Run from ~/linux-practice

mkdir -p projects/search-demo
echo 'secret pattern' > projects/search-demo/file.txt
grep -r 'pattern' projects

Prints changed output without modifying the file.

Run from ~/linux-practice

cd ~/linux-practice
echo -e 'Hello\nWorld\nHello World' > text.txt
sed 's/Hello/Hi/' text.txt
sed 's/Hello/Hi/g' text.txt

Shows only selected lines.

Run from ~/linux-practice

sed -n '2p' text.txt
sed -n '1,2p' text.txt

Changes the file and keeps a backup copy.

Run from ~/linux-practice

sed -i.bak 's/Hello/Hi/g' text.txt
cat text.txt
cat text.txt.bak

Prints columns and line numbers.

Run from ~/linux-practice

cd ~/linux-practice
echo -e 'Name Age City\nJohn 30 NYC\nJane 25 LA' > data.txt
awk '{print $1, $3}' data.txt
awk '{print NR, $0}' data.txt

Uses comma as a field separator and calculates values.

Run from ~/linux-practice

echo -e 'Product,Price,Quantity\nApple,1.50,100\nBanana,0.75,200' > inventory.csv
awk -F, 'NR>1 {print $1, $2 * $3}' inventory.csv

Accumulates a total and prints it at the end.

Run from ~/linux-practice

awk -F, 'NR>1 {total += $2 * $3} END {print total}' inventory.csv

Creates harmless test files.

Run from ~/linux-practice

cd ~/linux-practice
mkdir -p find-lab/subdir/nested
touch find-lab/file1.txt find-lab/file2.pdf find-lab/old.log find-lab/subdir/test.txt

Searches by name and type.

Run from ~/linux-practice

find find-lab -name '*.txt'
find find-lab -type f
find find-lab -type d
find find-lab -empty

Lists matching files and prints logs before any deletion.

Run from ~/linux-practice

find find-lab -name '*.txt' -exec ls -lh {} \;
find find-lab -name '*.log' -print

Deletes only the practice .log file after you have confirmed the match.

Run from ~/linux-practice

find find-lab -name '*.log' -delete

Changes permissions on your own practice file.

Run from ~/linux-practice

cd ~/linux-practice
touch permissions_demo.txt
chmod 644 permissions_demo.txt
ls -l permissions_demo.txt
chmod 600 permissions_demo.txt
ls -l permissions_demo.txt

Adds execute permission to a practice script.

Run from ~/linux-practice

echo 'echo Hello' > scripts/hello.sh
chmod +x scripts/hello.sh
./scripts/hello.sh

These examples explain SUID and sticky bit. Do not run them; Ubuntu already manages system permissions.

Run from do not run

chmod u+s /usr/bin/passwd
chmod +t /tmp

Shows your username, IDs, and groups.

Run from ~/linux-practice

cd ~/linux-practice
whoami
id
groups

Shows ownership on your file and reads user/group databases.

Run from ~/linux-practice

touch owned-by-me.txt
ls -l owned-by-me.txt
head -5 /etc/passwd
head -5 /etc/group

These change real system state. They are explained, not required for this safe course.

Run from advanced users only

sudo chown username:groupname file.txt
sudo adduser testlearner
sudo userdel -r testlearner

Shows current and system processes.

Run from ~/linux-practice

ps
ps aux | head -15
pgrep -l bash

Starts one harmless background process, captures its exact PID with $!, then stops and waits for that same process. This remains deterministic even when other jobs already exist.

Run from ~/linux-practice

cd ~/linux-practice
sleep 100 &
practice_pid=$!
echo "Started practice PID: $practice_pid"
jobs -l
kill "$practice_pid"
wait "$practice_pid" 2>/dev/null || true
jobs -l

Useful but broad. Prefer job number or exact PID while learning.

Run from ~/linux-practice

killall sleep
pkill -f 'sleep 200'

Reads common environment variables.

Run from ~/linux-practice

printenv | head -20
echo $HOME
echo $USER
echo $SHELL
echo $PATH

Creates and removes a temporary variable.

Run from ~/linux-practice

export MY_NAME='Linux Learner'
echo $MY_NAME
bash -c 'echo Child sees: $MY_NAME'
unset MY_NAME

Temporarily adds your practice bin folder to PATH.

Run from ~/linux-practice

mkdir -p ~/linux-practice/bin
export PATH="$HOME/linux-practice/bin:$PATH"
which ls
whereis bash
type cd

command -v is the portable way to find a command or shell builtin. command -V gives a fuller explanation, while env lists exported variables for the current process.

Run from ~/linux-practice

command -v ls
command -v cd
command -V cd
env | sort | head -20

Creates a friendly listing shortcut.

Run from ~/linux-practice

alias ll='ls -la'
ll
alias ll

Removes the temporary shortcut.

Run from ~/linux-practice

unalias ll
alias

Runs the original command even if an alias exists.

Run from ~/linux-practice

alias ls='ls --color=auto'
command ls
\ls

Shows recent commands.

Run from ~/linux-practice

history 10

Repeats the previous harmless echo command.

Run from ~/linux-practice

echo 'safe repeat demo'
!!

Clears current shell memory history. Explanation only for most learners.

Run from ~/linux-practice

history -c

Creates multiple practice files quickly.

Run from ~/linux-practice

echo file_{1..5}.txt
touch file_{1..5}.txt
ls file_*.txt

Shows common filename patterns.

Run from ~/linux-practice

mkdir -p glob-lab
cd glob-lab
touch a.txt b.txt c.txt 1.txt 22.txt abc.txt
echo *.txt
echo ?.txt
echo [ab].txt
cd ..

Removes only the glob-lab folder created in the sandbox.

Run from ~/linux-practice

rm -rf glob-lab

Shows two names for the same file data.

Run from ~/linux-practice

cd ~/linux-practice
echo 'Original content' > original.txt
ln original.txt hardlink.txt
ls -li original.txt hardlink.txt
echo 'Added line' >> original.txt
cat hardlink.txt

Creates and inspects a symbolic link.

Run from ~/linux-practice

echo 'Target content' > target.txt
ln -s target.txt symlink.txt
ls -l symlink.txt
readlink symlink.txt
cat symlink.txt

Demonstrates a broken symlink inside the practice folder.

Run from ~/linux-practice

rm target.txt
cat symlink.txt

Creates a folder to archive.

Run from ~/linux-practice

cd ~/linux-practice
mkdir -p archive-lab/docs
echo 'file1' > archive-lab/file1.txt
echo 'readme' > archive-lab/docs/README.txt

Creates a compressed tar archive and lists its contents.

Run from ~/linux-practice

mkdir -p backups
tar -czvf backups/archive-lab.tgz archive-lab
tar -tvf backups/archive-lab.tgz

Extracts into a dedicated restored folder.

Run from ~/linux-practice

mkdir -p restored
tar -xzvf backups/archive-lab.tgz -C restored
ls -R restored

Reads the beginning of your real .bashrc without changing it.

Run from ~/linux-practice

cat ~/.bashrc | head -30

Changes and restores the prompt only in the current shell.

Run from ~/linux-practice

OLD_PS1=$PS1
PS1='Practice> '
echo 'Prompt changed for this session'
PS1=$OLD_PS1

Sources aliases from a removable practice file.

Run from ~/linux-practice

echo "alias showdate='date +%Y-%m-%d'" >> ~/linux-practice/my_aliases
source ~/linux-practice/my_aliases
showdate
unalias showdate

This permanently modifies your real shell startup file. Explanation only in this course.

Run from do not run

echo "alias la='ls -A'" >> ~/.bashrc

Creates a complete mini project.

Run from ~/linux-practice

cd ~/linux-practice
mkdir -p final_project/{src,docs,bin} backups
cd final_project
echo 'main function' > src/main.c
echo '# README' > docs/README.md
cat << 'EOF' > bin/script.sh
#!/usr/bin/env bash
echo 'Processing...'
for f in src/*; do
  echo "Found: $f"
  wc -l "$f"
done
EOF
chmod +x bin/script.sh

Uses archive, find, grep, head, xargs, du, and script execution.

Run from ~/linux-practice/final_project

cd ~/linux-practice/final_project
tar -czvf ../backups/final-project-v1.tgz src docs bin
tar -tzf ../backups/final-project-v1.tgz
find . -name '*.sh' -exec ls -lh {} \;
grep -r 'function' .
head -2 docs/README.md
find . -type f \( -name '*.c' -o -name '*.sh' \) -print0 | xargs -0 wc -l
du -sh .
./bin/script.sh

Deletes only final_project inside the sandbox.

Run from ~/linux-practice

cd ~/linux-practice
rm -rf final_project

Shows size of the practice folder and its contents.

Run from ~/linux-practice

cd ~/linux-practice
du -sh
du -sh * 2>/dev/null

Shows root filesystem free space and type.

Run from ~/linux-practice

df -h /
df -hT /

Reads storage and mount information only.

Run from ~/linux-practice

lsblk
findmnt | head -20
mount | head -20

Searches and inspects packages without installing anything.

Run from ~/linux-practice

apt search 'text editor' | head -20
apt show nano | head -20
apt list --installed | head -20

Checks which common package-manager command is available without changing the system. Follow the APT examples only on Ubuntu, Debian, or their WSL distributions.

Run from anywhere

command -v apt || true
command -v dnf || true
command -v pacman || true
command -v zypper || true

Uses dpkg to inspect installed package information.

Run from ~/linux-practice

dpkg -l | head -20
dpkg -l | grep -i bash
dpkg -L bash | head -20

This changes the real Ubuntu system. It is optional and not part of the removable sandbox guarantee.

Run from advanced users only

sudo apt update
sudo apt install sl -y
sudo apt remove sl

Sends ICMP probes to a public address and the local loopback interface. A reply is useful evidence; no reply is inconclusive because networks and hosts may block ICMP.

Run from ~/linux-practice

ping -c 2 8.8.8.8
ping -c 1 localhost

Separates name lookup from ICMP reachability. If the IP address replies but name lookup fails, DNS is the likely layer to investigate. A failed ping alone does not prove the network is offline.

Run from ~/linux-practice

getent hosts example.com
ping -c 1 example.com
ping -c 1 1.1.1.1

Downloads into the sandbox downloads folder. -L follows redirects; -I fetches headers only.

Run from ~/linux-practice

mkdir -p ~/linux-practice/downloads
cd ~/linux-practice/downloads
curl -IL https://example.com
curl -L -o example.html https://example.com
head -5 example.html

Views addresses, routes, and listening ports.

Run from ~/linux-practice

ip addr show | head -30
ip route show
ss -tuln | head -20
hostname -I

Shows memory, uptime, and short virtual memory stats.

Run from ~/linux-practice

free -h
uptime
vmstat 1 2

Shows a non-interactive top snapshot and memory-heavy processes.

Run from ~/linux-practice

top -b -n 1 | head -20
ps aux --sort=-%mem | head -10

Reads recent logs only when systemd is running, then starts a repeating clock. This handles non-systemd distributions and WSL environments where systemd is disabled. Stop watch with Ctrl+C.

Run from ~/linux-practice

if command -v journalctl >/dev/null && [ "$(ps -p 1 -o comm=)" = systemd ]; then
  journalctl -n 20 --no-pager
else
  echo "systemd journal is not available in this environment"
fi
watch -n 2 date

Creates and runs a first script.

Run from ~/linux-practice

cd ~/linux-practice/scripts
cat << 'EOF' > hello.sh
#!/usr/bin/env bash
echo "Hello, $USER!"
echo "Today is $(date)"
echo "You are in $PWD"
EOF
chmod +x hello.sh
./hello.sh

Shows common script argument variables.

Run from ~/linux-practice

cat << 'EOF' > args.sh
#!/usr/bin/env bash
echo "Script name: $0"
echo "First argument: $1"
echo "All arguments: $@"
echo "Number of arguments: $#"
EOF
chmod +x args.sh
./args.sh one two three

Shows non-zero failure and zero success statuses.

Run from ~/linux-practice

ls /nonexistent
echo "Exit status: $?"
ls /bin/bash
echo "Exit status: $?"

Creates a basic conditional script.

Run from ~/linux-practice

cd ~/linux-practice/scripts
cat << 'EOF' > if_demo.sh
#!/usr/bin/env bash
num=${1:-10}
if [ "$num" -gt 10 ]; then
  echo "Greater than 10"
elif [ "$num" -eq 10 ]; then
  echo "Exactly 10"
else
  echo "Less than 10"
fi
EOF
chmod +x if_demo.sh
./if_demo.sh 25

Loops over fixed words. Saved in scripts/ alongside if_demo.sh.

Run from ~/linux-practice

cd ~/linux-practice/scripts
cat << 'EOF' > for_demo.sh
#!/usr/bin/env bash
for fruit in apple banana cherry; do
  echo "I like $fruit"
done
EOF
chmod +x for_demo.sh
./for_demo.sh

Matches one value against multiple patterns. Saved in scripts/ alongside the other demo scripts.

Run from ~/linux-practice

cd ~/linux-practice/scripts
cat << 'EOF' > case_demo.sh
#!/usr/bin/env bash
answer=${1:-yes}
case "$answer" in
  yes|y|YES|Y) echo "You agreed." ;;
  no|n|NO|N) echo "You disagreed." ;;
  *) echo "Invalid input" ;;
esac
EOF
chmod +x case_demo.sh
./case_demo.sh yes

Checks that the crontab command exists before listing entries, and distinguishes a missing tool from an empty or inaccessible user crontab. Scheduling also requires a working cron-compatible service.

Run from ~/linux-practice

if ! command -v crontab >/dev/null; then
  echo "crontab is not installed in this environment"
else
  crontab -l 2>/dev/null || echo "No user crontab exists, or access is unavailable"
fi

Simulates repeated scheduled work without editing crontab.

Run from ~/linux-practice

cd ~/linux-practice
mkdir -p logs
for i in {1..3}; do echo "Simulated run at $(date)" >> logs/schedule-demo.log; sleep 2; done
cat logs/schedule-demo.log

Removes the entire user crontab. Explanation only; do not use as course cleanup.

Run from do not run

crontab -r

Discovers command locations, shell builtins, and descriptions. Prefer command -v over which in scripts because command is provided by the shell.

Run from ~/linux-practice

command -v ls
command -V cd
whereis bash
type cd
whatis ls
apropos 'list directory' | head -10

Opens the ls manual. Press q to quit.

Run from ~/linux-practice

man ls

Installs plocate (the modern locate on Ubuntu 22.04+) and updates its database. Optional only.

Run from advanced users only

sudo apt install plocate -y
sudo updatedb
locate bashrc | head