CS102B - Lesson 1

Unix, Hello World, Github

Instructor: Professor Hong

Intros

  • Name, Major, Year
  • What do you hope to get out of this class?
  • How many of you have coded before? What languages?

A Bit About Computers

A computer consists of hardware that executes the software.
  • System Software - provides a user interface and tools that allow the user to access and use different components of the computer
  • Application Software - helps users solve problems and accomplish tasks

Programming Languages

  • High Level - more powerful instructions, portable, simpler to understand and use - C, C++
  • Low Level - machine languages and assembly languages

Programming Languages

  • Interpreted - the computer will run the code by reading through the lines of your code
  • Compiled - the computer will run a program that was optimized

Machine Code

  • This is what the computer "understands"
  • A computer "understands" a stream 1's and 0's.
    • bit - a single 0 or 1 in binary
    • byte - a sequence of 8 bits; can be represented as a number from 0 to 255
  • A compiler converts C code into machine readable instructions

Parts of a C Program

  • Consists of variables and functions
  • Function - a sequence of statements
  • Some functions are part of the C language itself and some are part of the libraries of ANSI C
  • You have to tell the compiler which functions you plan on using
  • Results in an executable file

Getting Started

There are several environments that one can use to develop:
  • unix machine
  • OS terminal - for Apple computers
  • Cygwin - for Windows
    • When installing, install everything that has gcc, g++, git, and its dependencies.
    • You can install everything if you want, but it will take a while and a lot of disk space.
  • Other IDEs (Integrated Development Environments)

For the purpose of this class, I will be using Cygwin.

Commands

man - shows you the man(ual) page of the command

Directories

  • cd directory -- change directory
    • cd ..
      • -- go back a directory
  • mkdir directory -- make directory
  • pwd -- tells you where you currently are

File Access

  • ls - list directories
    • ls -l -- lists your files in a long format
    • ls -a -- lists all files including those that begin with a dot
    • ls -latrh -- lists all files in long format, in reverse order of the modification time, in human-readable form (use man to read more

File Access (cont.)

  • mv filename1 filename2 -- moves a file; also renames a file
  • cp filename1 filename2 -- copies a file
  • rm filename -- removes a file
    • rm -rf * -- removes everything!! Make sure you back things up; we will do that later with Github
    • Note: * is a wildcard

File Access (cont.)

  • diff filename1 filename2 -- diffs 2 files
  • wc filename -- tells you how many lines, words, and characters are in a file
  • chmod options filename -- changes the read, write, and executable access for a file
    • If you're lazy, you can always do chmod 777 filename to enable all access for all types of users
  • touch filename -- creates a blank file or updates the timestamp of the file touched

Finding Stuff

  • ff -- find files anywhere on the system
  • grep string filename -- looks for a string in the files in the directory
    • Note: there are many useful flags that you can use to make this stronger; see man grep

Editors & Shell Scripts

Editors

There are various editors that you can use:
  • vim
  • emacs
  • notepad++
  • other IDEs (eclipse, etc.)

Note: Depending on the company you end up working for, you may not be able to install certain editors/IDE. You should learn one of the basics - vim or emacs.

vim Quick Guide

  • vim filename -- to start editing a file with vim
  • ESC :w -- write/save the file
  • ESC i -- insert before the character
  • ESC a -- insert after the character
  • ESC :q -- quit vim

Writing a Bash Shell Script


#!/bin/bash

mkdir new_folder
cd new_folder
touch new_file.txt
ls

Hello World