Command Line basics

When you work with GNU/Linux Operating Systems such as OSGeoLive, Ubuntu, etc., it is good to know how to work on the command line.

Don’t worry. It is not difficult to learn and you will discover that it is fun and very powerful.

In this quickstart you will learn some basic commands.

The following commands run from within a Terminal Emulator window.

Start a Terminal Emulator (QTerminal currently) from the Applications menu in the System Tools section. This gives you a Unix shell command prompt.

Where am I?

pwd shows the path of your current location.

pwd
/home/user

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You can ask all commands for help and get information on how they can be used and find out about additional options.

pwd --help
pwd: pwd [-LP]
  Print the name of the current working directory.

  Options:
    -L        print the value of $PWD if it names the current working
              directory
    -P        print the physical directory, without any symbolic links

  By default, `pwd' behaves as if `-L' were specified.

  Exit Status:
  Returns 0 unless an invalid option is given or the current directory cannot be read.

How to navigate in the file system?

First you should get to know how the file system under Linux is organized. The file system is organized in a tree. It starts with the / known as root directory. All files and directories are under the root directory (/).

The current user is « user » and has a home directory located at /home/user. Anytime you open a terminal window it will start in your home directory (see pwd).

You can easily navigate in the file system with the command cd.

cd / navigated to the root directory cd /home/user goes to your home directory same as cd ~

cd .. moves you one directory to the top, cd user goes from your current location to the home directory of user. This is not the same as /user

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Use the tab key to autocomplete the path while you are typing.

Create a directory

You have write access in your user-directory. You can create files and directories there. Next we will create a directory for some command line tests.

cd ~
mkdir demo - creates the directory demo
cd demo

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You have a command history. You can navigate in the history with the arrow up and down key.

How to create a new file

touch creates a new empty file.

cd ~/demo
touch hello.txt

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You can pipe the information from a command to a file i.e. the command history. history displays the command history. With the following command it can be saved in a file.

history > history.txt

Show me what is in a directory

You would like to know more about the content of a directory. ls is the program that gives you a lot of information.

  • ls lists all files and directories

  • ls -l shows a more detailed list of the files/directories with time, user access rights

  • ls -a also shows hidden files

  • ls -al you can combine the different options

  • ls -1 shows only the file names

cd ~/demo
ls -l

total 4
-rw-rw-r-- 1 user user   0 Dec 26 16:23 hello.txt
-rw-rw-r-- 1 user user 255 Dec 26 16:24 history.txt

Copy files and directories

You can copy files from one location to another.

Copy a file to a new file

cp hello.txt hello_again.txt

Copy a file to another directory

cp hello.txt /home/user/

Copy a whole directory to a new location (-R recursive)

cp -R /home/user/demo /tmp

Qui est sudo?

With sudo you can do things that you are normally not allowed to. sudo runs commands with the rights of the superuser also known as root With sudo you can i.e. install more software, administrate services, change access rights and more fun. You will see the use of sudo in some of the following commands.

Search and install programs

Show information about programs.

apt show postgis

Search for programs

apt search postgis

Install programs

sudo apt-get install sl

You will love the program sl. Run the new program with sl see also apt show sl.

Services

Some programms run as services like PostgreSQL, tomcat or Apache Webserver. You can start or stop the services.

Restart your Apache Service

sudo service apache2 restart

sudo service apache2 --help

sudo service apache2 status

How to edit files

You can either edit files in the terminal or open them with an external program like Geany.

In the terminal window you can use the vim editor (Vi IMproved). vim is very powerful and has many options.

Voir aussi

Open a file with vim:

vim /home/user/demo/hello.txt

  • press i to switch to the input mode

  • ESC leaves the input mode

  • :w saves your changes

  • :wq saves your changes and closes the file

  • :q closes the file

  • :q! closes the file without saving

Owner and access rights

Access rights define whether a user or group or others have access to a file and what sort of access is given. You can have read, write or excecute access.

Directories or files have an owner and a group definition. By default the creator of a file/directory is the owner. But this definition can be changed. You will learn this in the next section.

You can show the owner and group via ls -l

cd /home/user/demo
ls -l
-rw-rw-r-- 1 user user 122 Dec 26 16:11 history.txt

  • the initial character can be - for a file or d for directory

  • user is defined as the owner and the group

Access rights are listed at the beginning of the row:

  • r read

  • w write

  • x execute

  • first 3 letters for the owner

  • then next 3 letters for the group

  • followed by the last 3 letters for others

Change the owner with chown

sudo chown -R user:www-data /var/www/html/TBD

  • first pass the user then the group - like user:www-data

  • -R recursive

Change access rights with chmod

sudo chmod -R 777 /var/www/html/TBD

  • 777 everyone can do everything

  • -R recursive

    1. number: owner (u)

    1. number: group (g)

    1. number: other (o)

  • 4 read

  • 2 write

  • 1 execute

  • 660 - owner and group are allowed to read and write, other have no rights

  • 744 - owner can do everything, group and others can only read

or use it like this

sudo chmod -R u+rwx /var/www/html/TBD

  • u = user

  • g = group

  • o = other

  • a = all

  • +/- right: r = read / w = write / x = execute

Choses à essayer

Here are other commands you may try.

  • grep - search for a pattern in a text

  • history | grep cd

  • rm - remove a file

  • rmdir - remove an empty directory

  • mv - rename/move

  • head - show the beginning of a file

  • tail - show the end of a file

  • find - search for files in a directory hierarchy

  • locate - find files by name

Ensuite ?

You have learned some important commands and information to work with the command line. Hopefully you have discovered how powerful the command line is.