1. Chapter 11 Command-Line Master Class
Ubuntu Unleashed
Chapter 11
Command-Line Master Class

2. Why Use Command Line? You want to string multiple commands together
Some commands are only available through the shell
Most server installs have no GUI – if you want to run the server you must know CL
You're a Linux guru, or want to be.

3. Basic Commands 25 recommended commands... cat – print file contents
cd – change directories
chmod – changes file permissions
cp – copies files
du – shows disc usage
emacs – edit text files
find – find files
gcc – compiles some programs
grep – searches for a text string

4. Basic Commands cont. less – allows paging through long files
ln – creates links between files
locate – find files from an index
ls – list of files in current directory
25 recommended commands...continued
make – compiles and installs programs
man – displays manual pages
mv – move or rename files
ps – lists processes
rm – removes files

5. Basic Commands cont. ssh – secure shell client
tail – prints the last lines in a file
top – prints resource usage
vim – edits text files
which – prints the location of a command
xargs – executes commands from its input

6. Advanced cat cat – basic use – print file (on screen) Advanced use
Merge 2 or more files
cat myfile.txt myfile2.txt
Remove all but one blank line per line of text
cat -s myfile.txt
Number the output lines
cat -n myfile.txt
Use multiple switches
cat -sn myfile.txt

7. ADV chmod Switch -c Prints a list of changes on screen
chmod -c 777 myfile.txt will respond with “mode of 'myfile.txt' changed to 777”
Switch -R
Will change permissions of a directory and all files within
Switch --reference
Allows you to specify a file and apply its permissions
chmod --reference reference_file myfile.txt

8. ADV cp Two switches --parents
Copies full path of the file into the new directory
Lets you know where the file was copied from -u
Allows for synchronizing of files – will not overwrite newer data
cp -u myfile mybackupfile

9. du
du – disc usage
Prints size of each directory (and how much space the files take up) inside current directory du
du -a – prints the size of individual files, as well as directories
du -h – makes du “human readable” – puts output in megabytes
du -c – prints total size of files

10. find find command – underutilized due to too many options/switches
Basic use – find -name “*.txt”
Will return all .txt files within directory and subdirectories
to include case variations (upper/lower) replace -name with - iname
size switch
Find -name “*.txt” -size 100k (or +100k or -100k)
Can also add “not” “user” and “perm” (for permissions) options
Can get very complex

11. grep Another search tool Searches for text strings within files
grep “this text that I'm looking for” *
Will list filename and line of text - within directory
Use -r to search subdirectories
grep -r “this text” *
Invert search with -v
Grep -v “this text” myfile.txt
Will show any line of text from file that does NOT have the words “this text”

12. less Sometimes a better option than “cat”
Allows you to scroll through the material
Works like “man” pages (q to quit, etc)
less filename
Loads of switches (one for every letter of the alphabet, and more!)
Can even open a bash session from within “less” and then return.

13. ln Creating Links with ln
Two types of links – hard links and symbolic links (symlinks)
Every filename points to an “inode”, the absolute location of a file
Linux allows different filenames to point to a single inode – results in a hard link
Hard links share content and attributes – change one and the other changes as well
A symlink is a redirect to the actual file (think shortcut in windows terms)
It's a dumb pointer – you can link to nonexistent files, and you can link to directories
ln creates hard links by default – use ln -s to create symlinks

14. locate Ubuntu creates an index of all of your files every night
locate command searches this index, as opposed to “find”, which searches recursively through each directory
locate is much faster than find
It's more limited than find as far as parameters – can't search by size, permissions, etc
locate myfile.txt

15. Adv ls Lists files in current directory Switches
-a – includes hidden files
-h – uses human readable sizes
-l – uses long listing
-r – uses reverse order
-R – lists recursively
-s – shows sizes of files
--sort – sorts the listing by size/time/extension

16. tail tail can be used to view the last ten lines of a file
Mostly used to keep track of running log files – using -f parameter
tail -f mylogfile

17. top Lists usage of resources Fields - PID – the process ID
User – the owner of the process
PR – priority
NI – niceness
S – status
%CPU – CPU usage
%Mem – memory usage
Time+ – CPU time
Command – the command being run
Etc
Knowing a process ID allows you to “kill” the process

18. echo echo command At it's most basic it parrots text back at you
echo 'I am a wookie' will result in I am a wookie repeated on the next line
Can echo the value of a system or env variable
echo $PATH
echo can redirect to a file
echo 'I am a wookie' >> wookie.txt

19. End Chapter 11 We'll finish advanced command line next week
There will be lots of worksheets
It may get frustrating
Don't give up
It takes time to get used to dealing with command line
You don't have to be an expert in the first hour, day, week, month, year, etc

20. DOL and CCBY