Linux and the Shell Command Line

First - get your pi running

• Hook up
• Keyboard
• Mouse
• HDMI Cable
• Then hook up power and plug it in
  
  

Some Linux Shell Commands

There are a whole lot of Linux shell commands literally thousands.  And it is unlikely you will memorize them all, or even ever use them all.  And if you are used to using a point and click graphical user interface,  the terminal (shell) command line interface can be as confusing as the Word Cloud above.  But this will pass as you gain more experience.

We will cover a few (well more than a few) of the most important commands.

First some background

1. The default shell on the Raspberry Pi is bash.  A shell is the user interface program between the user (us) and the Kernel.
   
2. From man bash:   "Bash  is  an  sh-compatible  command language interpreter that executes
          commands read from the standard input or from a file.  Bash also incor‐
          porates useful features from the Korn and C shells (ksh and csh)."
3. bash will look for programs to run in $PATH:
   
   /home/pi/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/local/games:/usr/games
   

Second some very important pieces of information:

1. Linux commands and names are case sensitive foo is not the same as Foo, fOO, foO etc.
2. To run a command in your directories you need to type ./foo where foo is the command name
   

Information

• man - display a manual page
• apropos search for a relevant manual page
  
• pwd  - print working directory (show me where I am).  It's easy to loose track of the directory you are in.
• ps - process status
• df - show disk usage
• ip address - display the ip address of your pi
  
• ping - bounce a short message off another machine to see if it is there.
  

Directories

• cd - change working directory
• mkdir - make a new directory
• rmdir - remove an empty directory
  
• pushd - push a directory onto the directory stack.  This is so you can get back to where you came from.
  
• popd - pop the (top see switches) entry off the directory stack and goes there
  
• dirs - show the directory stack

Files

• nano - edit a file.
• ls - list the contents of a directory.  The -l switch shows more detail
  
• rm - remove (delete) a file
• cp - copy a file to a new file name or a new directory.
• mv - move a file to a different directory or change a file name.
• chmod - change a file's mode (permission) bits.
  
  

  Owner	group	other
  rwx	rwx	rwx
  421	421	421

• 700 is rwx for the owner nothing for everyone else
• 644 is rw for the owner, read only for everyone else
• 755 is rwx for the owner r x for everyone else.
  
• Or if you want to do it symbolically (the hard way in my opinion) u+rwx g+rx o+rx is the same as 755, or - to remove a permission o-rx to remove read and execute from other.
• touch - create an empty file, or update a file's times to now.
  
• more or less - display a file one screen at a time.
  
• cat - concatenate, or show a file

Control

• passwd - change your password
• sudo - become super user for a moment.   This is needed when installing programs and editing config files etc.
• apt-get update - update the repository information, install - install a new program
• halt - halt your pi safely
• echo - display what follows on the screen
• clear - clear the screen
• reboot - reboot your pi safely

Shell Special Keys

• | pipe, copy the output of one program to the input of another program.
• ls -l |grep fibble
  
• > redirect, redirect the output from a program to a file.
  
• Ctrl-C key - terminate the current process
• Tab key - fill in the rest of the command if possible.
• \  - escape the next character. 
  
• ls -l this is my file.txt will try to list the files this, is, my and file.txt.  ls -lthis\ is\ my\ file.txt will list the desired file info.
• A good reason not to use spaces in file names, but if they are encountered it can be dealt with.
  
• * - anything
• ls *foo*  will match all files that contain foo somewhere in their name.
  
• ~ - The current users home directory.
• ~/foo/bar is the same as /home/pi/foo/bar.  Assuming this is the pi user.
  

Simple Shell Scripts

• shell scripts.  You will often encounter several commands you use often or a command that is useful but you never remember where it is.  You can stick the commands in a file and then run the file.  EG.
• the file cpuTemp contains
• /opt/vc/bin/vcgencmd measure_temp
  
• alias

A larger list of CLI commands can be found on the VicPiMakers website.

Homework

• Install the screen capture program scrot using apt-get.
• Explore 5 of the commands above that we did not cover in detail.
• use scrot to capture 5 images of you using these commands.  1 for each command you choose.  You can learn how to use scrot using man scrot
  
• email those images to me.  deid@drsol.com
• create and experiment with your own shell script.  Email that script too.