0) How commands are written

command  [options]  [arguments]

# example:

ls -la /etc

• Use Tab to autocomplete, ↑/↓ to reuse history, Ctrl+C to stop a running command.

1) Navigation & paths

pwd                 # print current directory

ls                  # list files

ls -la              # list all (incl. hidden) with details

cd /path/to/dir     # change directory (absolute)

cd ..               # go up one level

cd ~                # go to your home

Tips: Linux is case-sensitive. ~ means your home; . = current dir; .. = parent.

2) Creating & managing files/folders

mkdir lab                       # make a folder

mkdir -p proj/src               # make nested folders

touch notes.txt                 # create empty file or update timestamp

cp a.txt b.txt                  # copy a → b

cp -r src/ backup/              # copy folder recursively

mv oldname.txt newname.txt      # rename (or move)

mv file.txt dir/                # move into dir

rm file.txt                     # delete file

rm -r tmpdir/                   # delete folder (recursive)

rm -ri tmpdir/                  # safer: ask before each delete

Safety: avoid sudo rm -rf /. When learning, prefer rm -ri.

3) Viewing files

cat file.txt            # print entire file

less file.txt           # paged view (q to quit, /search)

head -n 20 file.txt     # first 20 lines

tail -n 50 file.txt     # last 50 lines

tail -f app.log         # follow a growing log

nl file.txt             # show with line numbers

4) Finding files & searching text

find . -name "*.py"                     # find by name

find /var/log -type f -size +100M       # big log files

grep "ERROR" server.log                 # search text

grep -R "main(" src/                    # search recursively

grep -n "todo" *.md                     # show line numbers

Pipeline example:

dmesg | grep -i usb | tail -n 20

5) Redirection & pipes (superpower)

ls -l > list.txt            # write output to file (overwrite)

echo "hello" >> notes.txt   # append

wc -l < notes.txt           # feed file as input

cmd1 | cmd2 | cmd3          # pipe: output → input

somecmd | tee out.txt       # see on screen AND save to file

cmd > all.log 2>&1          # combine stdout+stderr into file

6) Permissions & ownership (quick)

ls -l                    # view perms: -rwxr-x---

chmod u+x run.sh         # add execute for owner

chmod 750 run.sh         # u=rwx,g=rx,o=-

chown user:group file    # change owner/group (needs sudo)

• r=4, w=2, x=1 → 7=rwx, 6=rw-, 5=r-x, 4=r--.

7) System & hardware info

whoami               # your username

id                   # uid/gid and groups

uname -a             # kernel/system

lsb_release -a       # distro info (Ubuntu/Debian)

date                 # current date & time

uptime               # how long the system is running

free -h              # RAM usage

df -h                # disk usage per mount

du -sh *             # sizes of items in current dir

lsblk                # disks/partitions

8) Processes & monitoring

ps aux                # all processes

top                   # live monitor (q to quit)

htop                  # nicer top (sudo apt install htop)

pgrep firefox         # find PIDs by name

kill 1234             # ask process 1234 to exit

kill -9 1234          # force kill (last resort)

9) Networking basics

ip a                          # show interfaces/IPs

ping -c 3 8.8.8.8             # test connectivity (3 pings)

curl -I https://example.com   # HTTP headers

wget https://example.com/x    # download a file

ss -tuna                      # open sockets (like netstat)

10) Package management (Ubuntu/Debian)

sudo apt update

sudo apt install tree git build-essential

sudo apt remove packagename

sudo apt upgrade

dpkg -l | less                # list installed packages

(For Fedora/RHEL use dnf; for Arch use pacman.)

11) Compression & archives

# tarballs

tar -czf project.tar.gz project/     # create gzip tar

tar -xzf project.tar.gz              # extract

# zip

zip -r project.zip project/          # zip folder

unzip project.zip                    # unzip

12) Users & groups (basics)

groups                # your groups

passwd                # change your password

# admin tasks (need sudo):

sudo adduser alice

sudo usermod -aG sudo alice

13) Shell quality-of-life

history                 # command history

!!                      # run previous command

!git                    # run last command starting with 'git'

echo $PATH              # where the shell searches for programs

alias ll='ls -alF'      # quick alias (put in ~/.bashrc)

source ~/.bashrc        # reload config

Quoting rules:

• "double quotes" keep spaces but expand $vars

• 'single quotes' keep text literally (no expansion)

14) Text processing one-liners (handy!)

cat file.txt | sort | uniq -c | sort -nr | head

# -> frequency count of lines (top N)

grep -R "ERROR" logs | cut -d: -f1 | sort | uniq -c | sort -nr | head

# -> which files have most ERROR lines

15) Mini-lab (30–40 minutes, do it now)

# setup sandbox

mkdir -p ~/lab/cli101 && cd ~/lab/cli101

echo -e "apple\nbanana\napple\ncherry" > fruits.txt

echo "Line one" > notes.txt

echo "Line two" >> notes.txt

# practice viewing/search

nl notes.txt

grep -n "apple" fruits.txt

# practice find + pipes

printf "log1\nlog2\n" | xargs -I{} sh -c 'echo "ERROR on {}" >> {}.txt'

grep -R "ERROR" . | tee errors_all.txt

# disk & system checks

df -h

du -sh *

# permissions

echo -e '#!/usr/bin/env bash\necho "Hello $USER"' > hello.sh

chmod 755 hello.sh

./hello.sh

# archive

tar -czf lab_backup.tgz .

ls -lh lab_backup.tgz

Quick exam-ready bullets

• Navigation: pwd, ls -la, cd, mkdir, cp -r, mv, rm -ri

• Viewing: cat, less, head, tail -f, nl

• Search: grep -R, find

• Pipes/redirect: |, >, >>, 2>&1, tee

• Permissions: ls -l, chmod, (concept of user/group/others)

• System/Proc: uname -a, free -h, df -h, top, ps aux, kill

• Network: ip a, ping, curl, wget, ss -tuna

• Packages: sudo apt update && sudo apt install <pkg>

• Archives: tar -czf, tar -xzf, zip, unzip

Want these as a 2-page printable PDF or a slide deck for your class? I can format and share it.