Unix is a family of computer operating systems that derive from the original Unix from Bell Labs.

Expect the output of every program to become the input to another, as yet unknown, program. Don't clutter output with extraneous information. Avoid stringently columnar or binary input formats. Don't insist on interactive input.

Locations in home
$HOME/bin	Local binaries
$HOME/etc	System configuration for local binaries
$HOME/games	Local game binaries
$HOME/include	Local C header files
$HOME/lib	Local libraries
$HOME/lib64	Local 64-bit libraries
$HOME/man	Local online manuals
$HOME/sbin	Local system binaries
$HOME/share	Local architecture-independent hierarchy
$HOME/src	Local source code

Primitives
ls	List files in the directory
cd	Change directory
rm	Remove file or directory(-r)
cp	Copy file or directory(-r)
mv	Move file or directory
wc	Count words in file
man	Read the manual
cat	Reads content of files sequentially
mkdir	Make new directory
date	Show system date
grep	Searches text for matches of a regular expression
tail	Displays the tail end of a file or data

Cheatsheet

Copy a file

; cp readme.txt documents/

Duplicate a file

; cp readme.txt readme.bak.txt

Copy a directory

; cp -a myMusic myMedia/

Duplicate a directory

; cp -a myMusic/ myMedia/

Move a file

; mv readme.txt documents/

Move a directory

; mv myMedia myMusic/

Rename a directory

; mv myMedia/ myMusic/

Merge directories

; rsync -a /images/ /images2/

Create a new file

; touch 'new file'

Create a new directory

; mkdir 'untitled folder'

Show file/directory size

; du -sh node_modules/

Show file/directory info

; stat readme.md

Open a file with the default program

; xdg-open file  # on Linux

Zip a directory

; zip -r archive_name.zip folder_to_compress

Unzip a directory

; unzip archive_name.zip

Peek files in a zip file

; unzip -l archive_name.zip

Remove a file

; rm my_useless_file
; rm -r my_useless_folder

List directory contents

; ls my_folder    # Simple

Tree view a directory and its subdirectories

; tree

Find a stale file

; find my_folder -mtime +5

View content of a file

; cat apps/settings.py

Search for a text

; grep -i "Query" file.txt

Make applications in ~/bin/ available from anywhere

Edit ~/.bashrc, when finished run source ~/.bashrc.

export PATH=$PATH:$HOME/bin

Pipes
ls > foo	Send output from ls into file foo
wc < foo	Receive input from file foo into wc
ls | wc	Connect output of ls into input of wc
Aliases

An alias let you define your own command names, so you can customize the command line, and make it work the way you want it to work. You can see the list of aliases with:

alias

To create an alias that will be there for you every time you start your computer, open ~/.bash_profile and add a line like:

alias left='uxnemu ~/roms/left.rom'

When finished, run the following line to apply your changes:

source ~/.bash_profile

You have just created a new alias called left.
"From each according to their stdout to each according to their stdin"
Usage

A usage statement is a printed summary of how to invoke a program from a shell prompt. It includes a description of the possible command-line arguments that the program might take. If a program is called with incorrect command-line arguments, it should print a usage statement to the terminal.

usage: ls [-a] [-F]

This program is called ls and can be called with no arguments, with one optional argument (ls -a or ls -F) or with two optional arguments (ls -a -F). In this particular case, the -a optional argument says to list hidden files as well as normal ones, and -F changes the way the output of the program is formatted.

Usage statements should be printed to "standard error" stderr, and not to stdout. Your usage statement should contain:

    The name of the program
    Every non-optional command-line argument your program takes
    Every optional command-line argument your program takes
    Any extra descriptive material that the user should know about.

Formatting guidelines

    The usage statement should always begin with the literal word usage in lower case, followed by a colon and space, followed by the rest of the usage message. So, the usage message starts with usage: .
    Every command-line argument in the usage statement should be a single word, with no spaces.
    The word representing a particular command-line argument should be descriptive. It should say what the command-line argument is supposed to represent, at least in general terms. Do not separate successive command-line arguments with commas or semicolons; just separate them with single spaces.

Optional arguments should always be surrounded by square brackets. Do not use square brackets for any other purpose in usage messages. Don't use anything but square brackets for this purpose. Square brackets mean that an argument is optional, always.

Optional "flags" (arguments that change the way the program works) should start with a dash. Very often (but not always) they will have a name which is a dash followed by a single letter, which identifies what it is.

Note that each optional argument gets its own set of square brackets. If an optional "flag" argument itself has arguments, put them inside the square brackets.
Notes

You shouldn't hard-code the program name into your program's source code. It won't make any difference in how it's displayed, but if you change the name of your program and don't change your usage message the usage message will be invalid. Instead, you should write your code so that the program name gets inserted into the usage message before printing. In C, the program name is argv[0] (the first element of the argv array) whereas in python it's sys.argv[0].