Domain 1: Linux Fundamentals (20%)¶

# Navigation
pwd                    # print working directory
ls                     # list directory contents
ls -la                 # detailed list including hidden files
cd /path               # change directory
cd ~                   # go to home directory
cd ..                  # go up one level
cd -                   # go to previous directory

# File operations
cp source dest         # copy file
cp -r src/ dest/       # copy directory recursively
mv source dest         # move or rename
rm file                # remove file
rm -r directory/       # remove directory recursively
mkdir directory        # create directory
mkdir -p path/to/dir   # create nested directories
touch file             # create empty file or update timestamp

# Viewing files
cat file               # display entire file
less file              # page through file (q to quit)
head -n 10 file        # first 10 lines
tail -n 10 file        # last 10 lines
tail -f file           # follow file in real-time (logs)

# grep - search for patterns
grep "pattern" file            # search in file
grep -i "pattern" file         # case-insensitive
grep -r "pattern" /path        # recursive search
grep -v "pattern" file         # exclude matching lines
grep -c "pattern" file         # count matches

# Other text tools
wc -l file                     # count lines
sort file                      # sort lines
uniq file                      # remove duplicates (sorted input)
cut -d: -f1 /etc/passwd        # extract field 1 with : delimiter

# I/O redirection
command > file                  # output to file (overwrite)
command >> file                 # output to file (append)
command 2> file                 # error output to file
command1 | command2             # pipe output to next command

# Examples
cat /etc/passwd | grep "bash"   # find bash users
ls -l | wc -l                   # count files

file filename          # determine file type
stat filename          # detailed file information
du -sh /path           # directory disk usage
df -h                  # filesystem disk space
which command          # find command location
man command            # manual page for command
command --help         # quick help text

nano filename          # open file
# Ctrl+O  - Save (Write Out)
# Ctrl+X  - Exit
# Ctrl+K  - Cut line
# Ctrl+U  - Paste (Uncut)
# Ctrl+W  - Search
# Ctrl+G  - Help

vim filename           # open file

# Modes:
# Normal mode (default) - navigation and commands
# Insert mode (i) - editing text
# Command mode (:) - file operations

# Key commands:
# i         - enter insert mode
# Esc       - return to normal mode
# :w        - save
# :q        - quit
# :wq       - save and quit
# :q!       - quit without saving
# dd        - delete line
# yy        - copy (yank) line
# p         - paste
# /pattern  - search forward
# u         - undo

apt update                     # update package lists
apt upgrade                    # upgrade installed packages
apt install package            # install package
apt remove package             # remove package
apt search keyword             # search for packages
apt list --installed           # list installed packages
dpkg -l                        # list installed (lower-level)
dpkg -i package.deb            # install local .deb file

dnf update                     # update all packages
dnf install package            # install package
dnf remove package             # remove package
dnf search keyword             # search for packages
dnf list installed             # list installed packages
rpm -qa                        # list installed (lower-level)
rpm -ivh package.rpm           # install local .rpm file

#!/bin/bash
# This is a comment

# Variables
NAME="World"
echo "Hello, $NAME"

# Command substitution
TODAY=$(date +%Y-%m-%d)
echo "Today is $TODAY"

# Conditionals
if [ -f /etc/hosts ]; then
    echo "File exists"
else
    echo "File not found"
fi

# Loops
for i in 1 2 3 4 5; do
    echo "Number: $i"
done

# While loop
COUNT=0
while [ $COUNT -lt 5 ]; do
    echo "Count: $COUNT"
    COUNT=$((COUNT + 1))
done

chmod +x script.sh             # make executable
./script.sh                    # run script
bash script.sh                 # run with bash (no execute needed)