Web Programming @ MIPT, 2015-2016

Server OS share

Unix	67.1%
Windows	32.9%
	W3Techs.com, 22 September 2015
Percentages of websites using various operating systems Note: a website may use more than one operating system

Software licenses

• GNU GPL - viral, "copyleft"
• GNU LGPL - less viral, "copyleft"
• MIT - simple, permissive, "do what you want"
• BSD - simple, permissive, "do what you want"
• Apache 2.0 - permissive, "do what you want", patent safe
• Public Domain - the most permissive, "do everything you want" (synonym: CC Zero)
• Exotic licenses for small projects: Beerware, WTFPL, etc.

UNIX history

Modern UNIX

• MacOS X (Darwin <- FreeBSD)
• Ubuntu (Linux)
• Fedora (Linux)
• Standard: POSIX 1003.1-2008 TC1

Use VirtualBox to try, or install on host (dangerous, but cool).

OS structure

1. Kernel
2. Middleware (system libraries)
   • libc
   • Drivers @ userland
3. Applications
   • Libraries
   • Shell
   • Core utilities
   • Window system (X11, Quartz, etc.)
   • Web browser

Installing software

Package Managers:

• Homebrew on MacOSX
• Chocolatey on Windows
• apt-get on Ubuntu, DNF on Fedora, etc.

Example:

			apt-get install chromium-browser
			brew install git
		

Terminal

Shell

• One uses a terminal emulator to access the shell
• Grandparent of all UNIX shells: Almquist shell (ash)
• Modern ash: dash
• Most popular and widespread shell: bash (Ubuntu, MacOS X)
• Hipster shells: zsh, fish
• POSIX standard

All scripts must carry a shebang, e.g.

			#!/bin/sh -e
		

Core utilities

• GNU Core Utilities on Linux
• BSD Base System on BSD/Darwin
• BusyBox on embedded systems (e.g., Android)
• POSIX standard

Example:

			$ ls -la
			total 32
			drwxr-xr-x  5 markhor  staff   170 22 Sep 21:01 .
			drwxr-xr-x  9 markhor  staff   306 22 Sep 20:59 ..
			-rw-r--r--@ 1 markhor  staff  7948 22 Sep 23:23 index.html
		

Standard streams

• stdout is for ordinary output (e.g., logs)
• stderr is for errors output
• stdin is for reading input
• More information on standard streams

UNIX signals

• Terminating a process softly means sending SIGTERM signal (15)
• Hard termination is done via SIGKILL (9)
• Ctrl-C sends SIGINT (2)
• More information on signals

Examples:

				kill -SIGTERM <pid>
				killall -15 <name>
			

UNIX pipes

• Pipe means redirecting process' stdout to other process' stdin
• Shells use "|" to designate pipes
• SIGPIPE is sent to prematurely terminate the chain

Examples:

				cat /path/to/file_list | sort | uniq | xargs file
				grep key /file | write <user>
			

Learn command-line environment

• Shell language: Advanced Bash Scripting Guide
• Coreutils examples: cli.learncodethehardway.org
• Interactive tutorial: codecademy.com
• Philosophy: The Art of UNIX Programming
• The most useful command: man

				man man
				man ls
			

• Second most useful command: history - prints your typed commands

Do not forget about tab completion!

Console text editors

• GNU Nano - the most easy to use and widespread (installed by default in Ubuntu, MacOS X)
• vim - widespread (installed by default almost anywhere)
• Recommending a text editor is a holy war
• Use something like Atom for casual code writing! Or an IDE.

Next steps

• Get UNIX (in virtual machine, as a second system, buy MacBook)
• Pass interactive tutorials: 1, 2, 3
• Download cheatsheets: 1, 2
• Continue to Git crash course