Using the Shell

• To use the shell of your Unix operating system, you will need to open up your terminal or console application. This application lets you enter commands using text. The terminal or console bypasses what is called the Graphical User Interface (GUI) of your computer so that you can speak to your software on a basic level. If you are using the Mac OSX, there is a default on your terminal that will not allow you to access shell scripting without turning it off. Open your Terminal Application through spotlight or go to the Applications Folder, then Utilities, then select "Terminal." Once you have opened Terminal, go to the Terminal option in your menu bar then select "Preferences." The preference dialogue window will open. Go to the shells open with area and select "Shells open with: command complete path". This will automatically have selected bin/bash, the shell with which we will work here.
  
  

First Script

• To run your first script. we are going to use the classic Hello World example. We will ask the computer to say a phrase back to us that we specify; in this case, the phrase hello world. Sign into your shell by typing:
  
  #! /bin/sh
  
  Then press "Enter" or "Return" to enter your shell. Once you have done this, you can enter your command. To enter your simple hello world request simply type:
  
  echo Hello World
  
  Your computer terminal will write Hello World back to you. You can type anything after the echo command and your computer will reply with that phrase.
  
  

Variables

• One of the features of the shell command line is the ability to assign variables to a command. You can add variables to almost any command to change what that command does. You can even make your own commands and assign a variable to it so that you can type a smaller version of the command and achieve the same result. We'll use the Hello World example again. You will make a variable before an = sign. Type:
  
  #! bin/sh
  
  The hit "Enter." Then type:
  
  I_MADE_A_MESSAGE="Hello World"
  
  With no spaces between the = and the "Hello World". To execute your variable type:
  
  echo $I_MADE_A_MESSAGE
  
  The dollar sign will make sure that the shell only echoes your Hello world message.
  
  If you ever need to remember a command simply type:
  
  man command