1. Chapter 12 Command-Line Master Class
Ubuntu Unleashed
Chapter 12
Command-Line Master Class

2. Redirect Output
Redirection – changes the standard input/output for commands
Standard input – keyboard
Standard output – monitor
To redirect output command line uses >
cat myfile.txt > mynewfile.txt
A new way to copy, but it will not warn you if you're about to overwrite a file
Can also cat 2 (or more) files into a new file or add 1 file to the end of another
cat file1 file2 > file3
Cat file1 >> file2

3. Redirect Input
Useful if you don't want to enter several lines of info with a command
I'll use the books example – making sure the same software is on 2 (or more ) PCs
First we redirect output to put a program list into a file – sudo dpkg --get selections > pkg.list
Now transfer this file to another PC and use the file as input – sudo dpkg --set selections < pkg.list
To finish – sudo apt-get -u dselect-upgrade

4. stdin – stdout - stderr Automatic (implied) input/output By default:
stdin – keyboard – assigned number 0
stdout – monitor – assigned number 1
stderr – monitor – assigned number 2
If you wanted to redirect error messages to a file that you could view at your leisure
program_name 2> error.log

5. Comparing files Finding differences – diff command
diff myfile.txt myfile2.txt
Will display any non-identical lines from the two files
Good for comparing current files with backups
Finding similarities – comm command
Comm myfile.txt myfile2.txt
Will display a large amount of info in 3 columns
column 1 – shows lines only in file 1
column 2 – shows lines only in file 2
column 3 – shows lines that are in both files

6. Combining commands Pipeline ( | )
Using a pipe between commands will turn the first commands output into the second commands input
cat myfile.txt myfile2.txt myfile3.txt | less
Would open 3 files on screen, but with the ability to scroll
Semicolon ( ; )
Runs the commands in order without input/output switching
ls;date;cat myfile.txt

7. Background/Boolean
Use an Ampersand ( & ) to run tasks in the background
Background tasks run without user input
You'll be given a PID
command_name &
Boolean Operators && and || (double-pipe)
Separate 2 commands with...
&& to only run the second command if the first works
command1 && command2
|| to only run second command if the first fails
command1 || command2

8. Environmental Variables
Variables loaded at login – think “settings” in Windows (and beyond)
Short list...
PWD – provides the path to your working directory
USER – will show current user
LANG – sets default language
SHELL – name and location of current shell
PATH – sets default locations of executable files
TERM – sets the type of terminal in use

9. Environmental Variables
To see the current value of any environmental variable, use echo $
echo $USER should display linuxes
To display all environmental variables
env command or printenv command
echo $PATH will show where Linux will look for executables

10. Text Editors Several to choose from Console based
emacs – GNU editing environment
nano – simple text editor
vim – updated version of “vi”
GUI based
gedit – GUI text editor – installed with Ubuntu
kate – a simple KDE based text editor
Kedit – another simple KDE editor

11. nano Create a new file nano newfilename.txt Edit an existing file
nano filename.txt
Simple commands initiated with the Ctrl key listed at bottom of screen
One of the easiest non_GUI text editors

12. vim Almost universally available in Linux/Unix
Very capable but confusingly cryptic
Press i to insert text
Press Esc key to exit insert mode
Press : (colon) to enter a command
Commands include (by no means a complete list)
x – deletes a character
dd – deletes a line
q – quits out of the program
w – saves the file
Run vimtutor for a 30 minute tutorial on vim

13. emacs Richard Stallman's editor (remember him?)
Editing environment – capable of more than editing – can create appointment book, calander, diary, etc
Most commands require Ctrl key
Ctrl + D – delete character
Ctrl + A – go to start of line
Ctrl + E – go to end of line
And many many many more

14. Compressed Files bunzip2 and gunzip – uncompress files
bzip2 and gzip – compress files
Tar – compress, uncompress and list
To create a compressed file from a directory
tar czf compressed_filename.tgz directoryname
c compresses the file
z creates gzip archive
f filename
t lists archive contents
To expand
tar zxf compressed_filename
x expands archive

15. byobu Open multiple consoles from one console
Useful when using a machine remotely
Instead of creating another ssh connection to open another console
Type byobu and hit enter – a second screen opens replacing first one
F2 – opens a new console
F3 – goes back to previous console
F4 – goes to next console
F6 - disconnect
F9 – opens help and config menu
F12 – locks screen
byobu creates a session that you can reconnect to and continue where you left off

16. Polite System Reset
Shutting down by holding the power button can be harmful to your operating system
Just sayin'
Any computer can (and will) freeze up
Shut your system down “politely”
Hold down SysRq + Alt keys and press
R – unRaw – takes keyboard control
E – tErminate – sends SIGTERM to all processes
I – kIll – sends SIGKILL to all remaining
S – Sync – flush data from memory to disc
U – Unmount – unmount all filesystems and remount as read only
B – reBoot – restarts the computer
Wait a few seconds between each keystroke

17. DOL and CCBY