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Terminal

/ - Root directory
~ - Home directory

^ - Control key.
M - Alt key.

CTRL + C - Stop running command.
CTRL + D - Close current shell session.
CTRL + L - Clear screen. (Scrolls you down in reality)

CTRL + A - Go to beginning of line.
CTRL + E - Go to end of line.
CTRL + F - Next word.
CTRL + B - Previous word.

ALT + Backspace - Delete last word.
ALT + Left / Right - Go to previous / next word.
CTRL + U - Delete whole line.

man COMMAND - Command help.
history - Lists all the commands used.
CTRL + R - Search command history. Hit again for previous command.

Information

cat /etc/os-release     # Linux version
df -h --total           # Show disk space in readable format
htop                    # CPU and RAM usage

Install

dpkg is a backend for apt-get, which is a backend for aptitude (GUI).

Packages

apt-cache search PACKAGE   # Search packages.
apt-cache madison PACKAGE  # List versions.

apt-get update             # Update the packages list.
apt-get install PACKAGE    # Install specified package.
apt-get upgrade            # Actually update the packages.

apt list --installed       # A list of installed packages.

apt-get remove PACKAGE     # Remove a specified package.
add-apt-repository REPO    # Add 3rd party repository or PPA (Personal Package Archive).

curl URL                   # Output the URL content.
wget "URL"                 # Download from URL.
sudo dpkg –i FILE_NAME     # Install downloaded file.

.deb

Install .deb packages from the terminal.

sudo dpkg -i <path/to/deb.deb>
sudo apt-get install -f

Find

grep -r 'string' directory_to_search      # List occurences of string in all files.
find /                                    # List root directory's content.
find / | grep FILE                        # Search the output.

sudo find / -iname FOLDER/FILE.ext    # Find case insensitive.
which PROGRAM                         # Find path to program.

Count

# Number of files
ls | wc -l

# Find all files with the given extensions
# in the specified folders, and count the number of lines.
find folder1 folder2 -name '*.js' -o -name '*.sql' | xargs wc -l

Utility

# Navigation
cd FOLDER   # Change directory
cd ..       # Go back one up
cd -        # Go back to last working directory
pwd         # Current path

# List
ls -a       # List all files, including hidden
ls -l       # List in a list format
ll          # Shorthand for ls -l
ls -lh      # Show file size

# Read
cat FILE       # Show the file content in terminal
less FILE      # View file content in the less program
head FILE      # Show first 10 lines
tail FILE      # Show last 10 lines
tail -f FILE   # Log in real time

# Create
mkdir FOLDER   # Create a folder
touch FILE     # Create a file

# Copy/Paste
cp PATH/FILE PATH/FILE   # Create a copy
mv PATH/FILE PATH/FILE   # Rename or Cut & Paste a file

# Delete
rm FOLDER/FILE   # Delete folder or file
rm -r FOLDER     # Delete a directory and its files

# Printing
echo TEXT      # print text
printf TEXT    # print formatted text
\n   # new line
\r   # carriage return, i.e. bring carret (cursor) to start of line

Processes

ps -ef                     # List all running processes.
ps -ef | grep <criteria>   # Find a specific process.
kill -9 <pid>              # Kill a process by id.

Environment Variables

PATH is an enviroment variable. It tells your machine where to search for program executables, so when you run your picc program you can just do picc instead of /usr/hitech/picc/9.82/bin/picc.

env            # List all variables.
echo "$HOME"   # Specific variable, in this case **$PATH**.

Add paths to ~/.profile to make them permanent. Paths require the bin, while variables don't.

The variable is not in the environment until you export it. Otherwise it's just a shell variable.

Paths are delimited with a colon :

# Method 1
vim ~/.profile # Edit this file.
PATH="$HOME/bin:$PATH" # Find this line.
PATH="$HOME/bin:$PATH:/usr/hitech/picc/9.82/bin" # Change it into this.
# It appends the new path to the existing system ones, just for this user.

# Method 2 - Shorthand to avoid editing manually.
export PATH="$PATH:/usr/hitech/picc/9.82/bin" # export <VARIABLE>="<VALUE>"

Password Generator

Generate a random 14 character password by using the linux /dev/urandom file, a stream of mashed system data.

cat /dev/urandom | env LC_CTYPE=C tr -dc a-zA-Z0-9 | head -c 14

Ubuntu on Windows

C:\Users\User\AppData\Local\lxss\home\user - Filesystem location.

cd /mnt/ - Navigate to My Computer (C:, D:).

How to Compile and Run a C Program

# Create file
touch hello.c

# Edit file
vim hello.c

Paste this C code in the file.

#include <stdio.h>

main() {
    printf("Hello World\n");
}
# Compile the code into hello program
gcc -o hello hello.c

# Run the program
./hello