Gnome
When you log in to the department Linux system using the ThinLinc client you will be usingthe Gnome graphical desktop environment.
The Gnome terminal
You can open a terminal in two ways:
- From the Applicatinos menu at the top left of the desktop: Applications → Accessories → Terminal.
- By pressing the keyboard shorcut CTRL + ALT + T .
After a few seconds a new terminal window should open.
In the upper left corner of the white area of the terminal window you seeabcd1234@arrhenius:~$
. This it the shell prompt with your username on the formabcd1234
and the name of the Linux server you areconnected to, in this example arrhenius
. The shell prompt you see might bedifferent.
The shell prompt
In the above example, the prompt shows the username of the logged in user abcd1234
together with the name of the physical Linux server arrhenius
used. You shouldsee your own user name. If you are logged into a different physical Linux serveryou will also see a different server name in the prompt.
It is also possible to tweak the prompt to show custominformation such as your username, local time etc.
Since the appearance of the shell prompt might vary, in all further instructions $
will be used to refer tothe Linux shell prompt. In the instructions, interaction withthe Linux shell in the terminal will be presented in a box like this.
$
Your username (whoami)
Every user on the Linux system has a unique username. The whoami
command will show your username.Type whoami
at the shell prompt.
$ whoami
Press enter to execute the command. Now the result will be printed on the nextline in the terminal and a new shell prompt will appear on the line after that.
$ whoamiabcd1234$
In the above example the username of the logged in user abcd234
is printed asthe result of the whoami
command.
Username
In all examples and instructions you should replace abcd1234
with your actual username.
Print working directory (pwd)
The shell has a concept of a current working directory. The pwd
(print workingdirectory) commands prints the full path of the current working directory.
Type pwd
at the shell prompt.
$ pwd
Press enter to execute the command.
$ pwd/home/abcd1234$
In the above example the current working directory /home/abcd1234
is printedas the result of the pwd
command.
Home directory
On the Linux system each user has a private home directory to where she/hecan save files and create sub directories.
When you first log in to the Linux system the home directory will be used as thecurrent working directory in the shell.
For user abcd1234
the full path to the home directory is /home/abcd1234
.
List files and directories (ls)
To list the files and directories in the current working directory the ls
command can be used. The name ls
is a short form of list (files).
Type ls
at the shell prompt.
$ ls
Press enter to execute the ls
command. You should see something similar to thebelow as result but you might see other files and folders listed.
$ lsfoo.txt Desktop public_html$
In the above example the only content in the current working directory is thetext file foo.txt
and two sub directories Desktop
and public_html
. You may seemany more directories and files.
Distinguish between files and folders (ls -F)
To get some more information about files and folder various options can be givento the ls
command. One useful option is -F
that marks directorieswith a trailing slash /
.
$ ls -Ffoo.txt Desktop/ public_html/$
Visualize a directory as a tree
The tree
command displays the contents of the current directory andsubdirectories as a tree structure.
$ tree
The output takes a graphical form which will resemble the following example:
.├── README.md├── one.txt├── sub│ └── three.txt└── two.txt1 directory, 4 files
In the above example, there are three files (README.md
, one.txt
andtwo.txt
) and one sub directory (sub
) in the current working directory. Inthe sub directory sub
there is a single file three.txt
.
You can provide three
with the path to a directory to visualize its content.
$ tree subsub/└── three.txt0 directories, 1 file
Change directory (cd)
The cd
command navigates to a different folder. The name cd
means change directory.
First print the current working directory.
$ pwd/home/abcd1234$
To navigate to the Desktop
folder, type cd Desktop
at the shell prompt and pressenter.
$ pwd/home/abcd1234$ cd Desktop$
Now, execute the pwd command.
$ pwd/home/abcd1234$ cd Desktop$ pwd/home/abcd1234/Desktop$
Note how the current working directory changed from /home/abcd1234
to/home/abcd1234/Desktop
as the result of the cd Desktop
command.
The directory above the current working directory can be referred to using ..
. To navigate to the parent directory, type cd ..
and press enter.
$ pwd/home/abcd1234$ cd Desktop$ pwd/home/abcd1234/Desktop$ cd ..$
Now, execute the pwd
command again.
$ pwd$ /home/abcd1234$ cd Desktop$ pwd/home/abcd1234/Desktop$ cd ..$ pwd/home/abcd1234$
Note how the current working directory changed back from /home/abcd1234/Desktop
to /home/abcd1234
as the result of the cd ..
command.
Print content of file to the terminal (cat)
The cat
command can be used to print the content of a file to the terminal.
Assume you have the following file named foo.txt
in the current working directory.
The first line of the file.The third line. The second line is empty.The last line of the file.
You can now print the content of foo.txt
to the terminal using the cat
command.
$ cat foo.txtThe first line of the file.The third line. The second line is empty.The last line of the file.$
The name cat
is a short formof concatenate which means tojoin together. If more than one argument is given to cat
the contents of theprovided files will be joined together and printed to the terminal.
In the below example cat
is used to concatenate the file foo.txt
with itself.
$ cat foo.txt foo.txtThe first line of the file.The third line. The second line is empty.The last line of the file.The first line of the file.The third line. The second line is empty.The last line of the file.$
One useful option to the cat
command is -n
which prefixes each line with a line number.
$ cat -n foo.txt 1The first line of the file. 2 3The third line. The second line is empty. 4The last line of the file.$
Count words, lines and bytes (wc)
The wc
command counts the number of words, lines and bytes.
$ wc foo.txt 4 20 98$
In the above example we see that the file foo.txt
contains for lines, 20 words and 98 bytes.
Filter (grep)
The grep
command searches its input for a pattern and prints all lines in theinput that contains that pattern.
To search for the the string X
in the input type grep X
at the shell promptand press enter.
$ grep X
Note that we don’t get back the shell prompt. This is because the grep
command is still running waiting for input.The grep
command will now read input from the terminal and print back alllines containing the character X
.
Now type Hello
and press enter.
$ grep XHello
There is no X
in the string Hello
and therefore grep
will not print back the string Hello
to the terminal.
Type Hello mr X
and press enter and watch what happens.
$ grep XHelloHello mr XHello mr X
Once you type Hello mr X
the grep
command will print Hello mr X
right back tothe terminal since it contains a matching X
.
Lets try a few more lines and observe what happens.
$ grep XHelloHello mr XHello mr XabcabcXdefabcXdefxxx
Only lines containing a matching X
will be echoed back to the terminal.
No more input
To tell grep
that you are done (no more input), press Ctrl D
(press and holddown the control key and while you still hold down the control key press theD key).
Press Ctrl D
. Now grep
terminates and you get back to the shell prompt.
$ grep XHelloHello mr XHello mr XabcabcXdefabcXdefABC$
To filter the lines i a file, the name of the file can be given together with a search pattern to grep
.
Assume you have the file foo.txt
in your current directory.
$ cat foo.txtThe first line of the file.The third line. The second line is empty.The last line of the file.$
In the below example only lines containing of
in the file foo.txt
will be printed to the terminal.
$ grep of foo.txtThe first line of the file.The last line of the file.$
Filter the output of ls using grep (ls | grep)
The usefulness of grep
might not obvious at this point. To make grep
usefulwe will combine grep
with ls
to filter the output of ls
.
First we use ls
to list all files and folders.
$ lsfoo.txt Desktop public_html$
If we are only interested in files (and folders) with names ending in .txt
wecan combine ls
and grep
to using the pipe character |
.
$ ls | grep .txtfoo.txt$
In the above example, first the ls
command exectutes but it does not print itsresult back to the terminal. Instead, the result of the ls
command becomes theinput to the grep
command. The only file or folder name containing .txt
isfoo.txt
.
Piping commands togehter
Using the pipe character |
the output of the command to the left becomes theinput to the command to the right. This is called piping the two commandstogether.
Compressed file arhives (tarballs)
It is often useful to compress multiple files and folders into a single filethat can later be decompressed and expanded to get back the original files andfolders. There exists many file formats for compressed file archives.
- Windows users commonly use the zip file format.
- Unix users commonly use the tar file format.
Tarball
The name tarball is often used to refer to a tar archive file.
Download the following gziped compressed tar archive (tarball) to your home folder:
- archive.tar.gz
Verify that you have the tarball in your current working directory
From the terminal, make sure you have the downloaded tarball in the currentworking directory.
$ ls | grep .tararchive.tar.gz$
In the above example the output of ls
is piped together with grep
to filter theoutput of ls
to only print any files (or folders) containing .tar
. Youshould see archive.tar.gz
among the results.
Sneak peek inside a tarball (tar tf)
To see the contents of a tarball without extracting all the files you can usetar with options t
and f
.
$ tar tf archive.tar.gzarchive/archive/large.txtarchive/small.txtarchive/sub_folder/archive/sub_folder/info.txt$
In the above example we see that the tarball archive.tar.gz
contains the toplevel directory archive
with sub folder sub_folder
. In the top level directoryarchive
there are two files (large.txt
and small.txt
) and in the sub foldersub_folder
there is a single file (small.txt
).
Unpack a tarball (tar xvfz)
To unpack and extract the contents of a gzipped tarball we need to use the xvfz
options together with the tar
command.
$ tar xvfz archive.tar.gzx archive/x archive/large.txtx archive/small.txtx archive/sub_folder/x archive/sub_folder/info.txt$
Now the tarball have been unpacked. Use ls
to see what happened to the currentworking directory.
$ ls | grep archivearchivearchive.tar.gz$
In the above example we now have a new directory named archive
inside thecurrent working directory.
Use cd
to “step inside” the archive
directory and then ls -F
to list thecontent.
$ cd archive$ ls -Flarge.txtsmall.txtsub_folder/$
Using the -R
option ls
will be run recursively stepping inside every sub-directory.
$ ls -Rlarge.txtsmall.txtsub_folder./sub_folder:info.txt$
In the result printed by ls -R
a single period .
means the current workingdirectory.
Print text back to the terminal (echo)
To print anything to the terminal simply type echo
followed by the text you wantto print.
$ echo HelloHello$
Note that HELLO
is echoed back to the terminal as the result of executing theecho Hello
command before the shell prints the next command prompt.
Shell variables
The shell can set and read variables. Sometimes it is useful to use the value ofa built-in shell variable to make a command more generic and/or portable.
Remember that the command woami
can be used to print your username.
$ whoamiabcd1234$
$USER
An alternative to woami
is to use echo together with the shell variableUSER
. In order for echo
to know if you want to print the string "USER"
orthe value of the shell variable USER
shell variables must be prefixed with $
or enclosed within ${ }
.
$ echo Hello USERHello USER$ echo Hello $USERHello abcd1234$ echo Hello ${USER}Hello abcd1234$
$HOME
Another useful shell variable is HOME
with the full path to the home directoryfor the logged in user.
$ echo $HOME/home/abcd1234$
Command history
Often you type and run a command in the terminal and later you wants to run thevery same command again. To prevent you from having to type the same thing againthe shell keeps a history of executed command. To navigate the history, simplypress the up-arrow to move backwards in history and press the down-arrow to moveforward in history.
Try the following command in the terminal.
$ pwd/home/abcd1234$
And now this command.
$ whoamiabcd1234$
If you want to repeat the whoami
command, simply press the up-arrow key once.Instead if you wish to run the pwd
command again, press the up-arrow key twice.
Reading manual pages (man)
For more information about command you can always refer to the correspondingbuilt in manual page. For example, to read the manual page for the ls
commandsimply type man ls
and press enter at the shell prompt.
$ man ls
This will print the manual one page at a time to the terminal. To view the nextpage, press the space bar. To quit, press q.
To learn more about the build in manual pages read the manual page about the mancommand.
$ man man
A summary of usefull controll keys when reading man pages.
Key | Behaviour |
---|---|
q | Quit and get back to the terminal |
Space bar or F | Move forward one page |
D | Move forward half a page |
B | Move backwards one page |
U | Move backwards half a page |
Learn more
To learn more about the Ubuntu Linux shell:
To learn more about tar file archives (tarballs):