Homework & Practical

• Let’s go through it• Does anyone not have access to the wiki?• Questions?

Corporate Environment

• We only get 2 years with you (pending name change and bachelor’s degrees)

• I have about 17 more classes to help you become a better IT professional

• So• If you don’t have everything current, I will bug

you for it as if I was your boss

Corporate Environment• This means, when class starts, if I am missing

something from you, I will ask you to work on the missing assignment before the practical

• This course builds on everything before it. If you fall behind, you won’t understand what we’re doing

• I will ask you about it in class• I will email you• I will bother you and bother you and bother you• So please do your work

Today

• Paths– Absolute– Relative

• The Shell– Look and feel

Paths• So far we have been dealing with things in our

home folder• ls • cp teams.txt scratch.txt• These things are all using the relative path• The relative path is how to get to something on a

system (file, command, etc…) from where you are right now

• Those files were in the student user’s home dir and as we were there too we didn’t have to provide any more info

So Relative Path

• Because we are automatically taken to tom’s home directory (or /home/tom), we are in the same directory as desktop

• So our path is the name of the file• This is akin to your desktop in Windows• People clutter their desktops with files– You can directly access them by clicking on them– It’s messy and people will judge you when they

see it

Remember Tom?

• If ‘tom’ was our username:

Absolute Path

• When reading guides you will usually encounter absolute paths

• These always start with a /• /home/tom• /home/tom/documents• /home/student• /home/student/teams.txt• /etc/httpd/conf/httpd.conf

Absolute Paths• Always start with a /• These lead down the “tree” to the specific

location of a resource (file/command/whatever)

• So /home/student/teams.txt means start at / (the highest or top-level directory)

• Go into the home folder• Go into the student folder• Access the teams.txt file

Relative Paths

• Relative paths are more confusing• I will use convoluted examples• Usually, they’re only used in very simple

situations– Going/accessing one/two levels (up or down)

• Two notations– . means “right here”– .. Means “up one level”

Relative Complexity

• If you cannot access them directly in your home folder, they’re in another folder/directory

• In the command line, to access something that’s not in your immediate directory, you have to tell the shell where to look

• For example: /sbin is not in our $PATH• So if we want to use the ip command, we have

to tell the shell where to go../../sbin/ip

..

• We can use .. to access one directory level above ours– And we can chain them together (as the last slide

showed)• Most used with the cd command to ‘change

directory’• cd ..• Would take us from /home/tom to /home

Side by Side• Absolute path vs relative path• [student@it136centos58vm ~]$ cat /etc/profile• Which way is used above?

• [student@it136centos58vm ~]$ cat ../../etc/profile• Which way is used above?

• [student@it136centos58vm ~]$ cd /etc• [student@it136centos58vm etc]$ cat profile• Which way is used above?

Mapped Out (Absolute)• Absolute path• [student@it136centos58vm ~]$ cat /etc/profile• The shell sees the leading / in /etc/profile and

immediately starts at the top, then moves down

Mapped Out (Relative)• Relative path – cat ../../etc/profile• [student@it136centos58vm ~]$ cat ../../etc/profile• The shell starts in /home/student, moves up to

/home, moves up to /, then moves down to /etc, and then to the /etc/profile

Full Linux Directory Structure

Another Look The relative path has to reflect our new position

Assuming we want to access the ‘text’ file Where We Are Relative Path /home/tom/documents text /home/tom documents/text /home tom/documents/text

Does ‘Where We Are’ look familiar? It’s the Absolute path Why?

One Last Time

Absolute Path /home/student /var/log/messages /etc/profile / /dev/sda1

Relative Path ../../bin log/messages file ../usr/../var/log ~

The Shell

• The shell is what we type in, and get response from• We’re working with the ‘Bash’ shell– BASH – Bourne Again Shell (/bin/bash)– SH – Bourne Shell (/bin/sh)– ZSH – Z Shell (/bin/zsh)– CSH – C Shell (/bin/csh)– And more…

• Each one does things just a little differently• Bash is the current standard but ZSH is “supposed”

to extend it

Look and Feel

• [student@it136centos58vm ~]$ lx• bash: lx: command not found• [student@it136centos58vm ~]$ ls /notThere• ls: /notThere: No such file or directory• [student@it136centos58vm ~]$ ls –e /home• ls: invalid option – e• Try ‘ls --help’ for more information• Bash tries to be intelligent and tell us where the

error is

Bash Auto-Complete• [student@it136centos58vm ~]$ ca<tab><tab>• cadaver captoinfo cat• call card catchsegv• callercase• [student@it136centos58vm ~]$ cat tea<tab><tab>• [student@it136centos58vm ~]$ cat teams<tab><tab>• teams2.txt teams.txt• [student@it136centos58vm ~]$ cat teams• Through the ‘command’ and ‘argument’ sections of our

model, the Bash shell will show us what we can use

Colors

• [student@it136centos58vm ~]$ ls• folder script.sh teams2.txt

teams.txt• So we see– Folders/directories as blue– Scripts (collections of commands in a file to be run

together) as green– Files as black

History

• [student@it136centos58vm ~]$ <up>• [student@it136centos58vm ~]$ ls• ls was the last command we ran• We can keep pressing up to go through all the

commands we have run since the last time we cleared the history

• This is very useful for fixing errors

Fix It

• [student@it136centos58vm ~]$ cat /etc/passswd

• cat: /etc/passswd: No such file or directory• [student@it136centos58vm ~]$ <up>• [student@it136centos58vm ~]$ cat

/etc/passswd <arrow left twice, backspace once>

• [student@it136centos58vm ~]$ cat /etc/passwd

Getting Unstuck

• Shell unresponsive?• Try:– Pressing enter a few times– Pressing the q key– Pressing ctrl+z or ctrl+c– Pressing the escape key

• If you enter a command and you see > the shell is waiting for additional flags/args

Own Study

• Questions?

• Paths – Sobell Ch 4 – The Filesystem (81-89)• Shell – Sobell Ch 5 – The Shell (125-133)