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Introduction

The command line (or "terminal" or "command prompt") is a window where you can type commands. In gNewSense you can start using the command line by clicking Applications -> Accessories -> Terminal. You may also use the command line if you choose to run your computer without starting the window manager.

GNU Bash is the default language interpreter for gNewSense and many other GNU/Linux distributions. An understanding of it and how to program shell scripts is wise. Please see manual available online.

With all of the pretty graphics in GNU/Linux, you may wonder why people still use the command line. Well, for starters, it's fast! Installing new software, renaming a bunch of files, resizing all of the images in a directory, or even simply moving from directory to directory looking at your files, all of these can be done with a single command in a terminal window.

The command line is great for automation. Just type in what you want the computer to do, press enter, and go make a sandwich. For example, by using the command line, you can tell your computer to download a file, and when it finishes, shutdown. Then you can go to sleep, download the file, AND save electricity. Convenience!

And using the command line looks cool. I recommend changing the color settings of the terminal to be bright green text on a black background. Even if you have no idea what you are doing, the people who see you with that window open will look upon you with awe.

With practice you might decide that you prefer to do things using the command line instead of with the mouse. You may even find yourself saying, "Gee, that was so easy to do when I used the command line! Why can't things be this easy in other operating systems??"

Documentation

If you want to have information on the command mycommand, you may type:

 man mycommand

This will provides you the mycommand definition and options. At the bottom are references to commands with a number, like in iwconfig(8). If you want to read this specific documentation, for this example, type:

 man 8 iwconfig

Sometimes, especially for GNU software, more detailled documentation is available through info formatted files. For this kind of documentation, you should instead type:

 info mycommand

If you just want to have a short list of most useful commands or when previous commands were unsuccessful, type:

 mycommand --help

Browsing Filesystem

pwd

To know where you are in the directory structure, type:

 pwd

ls

To list files and directories in the current directory:

 ls

You can also use options:

 ls -a  # lists all files and folders including hidden ones, whose name begin with a point
 ls -l  # lists files and folders with rights, size and other useful informations
 ls -hl # same as above with human readable sizes
 ls -R  # lists files and folders recursively
 ls -sh # lists files and folders and prints their size in KB, MB, etc

ls command is particularly powerful with the use of grep and piping |:

 ls -al | grep ".jpg" # lists all files and directories, even hidden, which contains .jpg (case sensitive) in their name
 ls | grep -i "gnu"   # lists files and directories which contains GNU or gnu or GnU, etc (case insensitive) in their name

cd

To change directory:

 cd mydestination
 cd .. # to go to the parent directory of current directory
 cd /  # to go to filesystem base directory, which has no parent directory
 cd ~  # to go to your personal home folder, /home/myusername

Files and directories movements

cp

To copy a single file or directory:

 cp myfile destination
 cp -R mydirectory destination   # copies directory AND its content to destination
 cp -u myfile destination        # updates destination content
 cp -v mydirectory destination   # be verbose
 cp -R mydirectory/* destination # copies all the content of directory to destination
 cp -R .* destination            # copies all the content of current directory, including hidden files, to destination

To copy several files or folders:

 cp myfile1 myfile2 myfile3 destination

mv

To move a file or directory:

 mv myfile destination
 mv -u myfile destination      # updates destination content
 mv -v mydirectory destination # be verbose

Creation and Deletion

touch

To create a file:

 touch myfile

mkdir

To create a directory:

 mkdir mydirectory
 mkdir -p path/mydirectory # creates directories composing path if they don't already exist, then creates mydirectory

rm

Remove a file or folder:

 rm file
 rm *               # removes all files in current directory
 rm -R mydirectory  # removes mydirectory
 rm -Rf mydirectory # forces mydirectory removal
 rm -i *.jpg        # asks you for each file ending with .jpg if you want to remove it

rmdir

Remove an empty directory:

 rmdir mydirectory

Shortcut/Symlink

To create a symbolic link (shortcut) to a file or folder:

 ln -s path/myfile linkname

Print file content

cat

To print the entire content of a file directly in the command-line:

 cat myfile

less

To see a file with less file reader:

 less myfile

Press q to exit.

less let you browse the file from top to bottom, that is useful for big files, for which cat will only let you see the bottom.

To find "something" in a file you are reading with less, type:

 /something

type n to find next occurence of "something".

You can also browse two files, one after the other:

 less myfile1 myfile2

To read myfile2, type this when you have finished reading myfile1:

 :n

Edit file content

There are three well known command-line editors: nano, Emacs and vi.nano is easier while Emacs and vi are more powerful.

Nano

To edit a file using nano, just do:

 nano myfile

Save by pressing both ctrl and O keys.
Quit by pressing both ctrl and X keys.

GNU Emacs

To edit a file using GNU Emacs, do:

 emacs myfile

Save by pressing ctrl-x then ctrl-s.
Quit (and save) by pressing ctrl-x then ctrl-c.
Find "something" by pressing ctrl-s, then type something. Press ctrl-s another time for next occurence.
Find "something" and replace it with "whatever" in the entire file by pressing ctrl-x, then type replace-regexp and press Return. Type something then press Return, type whatever then press Return.

Vi

To edit a file using vi, do:

 vi myfile

To write something, you need to press i (for insert) key.
Save by pressing esc key, then type :w.
Quit by pressing esc key, then type :q.
Save and quit by pressing esc key, then type :wq.
Quit without saving by pressing esc key, then type :q!.

Find "something" by pressing esc key, then /something like with less command. Press return for next occurence.
Find "something" and replace it with "whatever" in the entire file by pressing esc key, then type s/something/whatever/g like with sed command.

Find files

To find files and folders on GNU/Linux, you can use either find or locate commands. The latter is faster but requires to build a database.

Find

To find files or folders which name contains "photo" (case sensitive), type:

 find -name "*photo*"
 find -iname "*photo*" # for "photo", "PHOTO", "PhOtOs", etc (case insensitive)
 find -mtime -3        # for files and folders modified less than 3 days ago

Sometimes, you have no read access on directories being searched. In this case, the following command may be helpful:

 find / -iname "libc*" 2>/dev/null

To combine criteria, use -a (AND) or -o (OR) inside brackets:

 find . \( -iname "*photo*" -a -mtime -3 \)

You can also find files or folders that do not respect a criteria, by using ! character:

 find . \( -iname "*photo*" -a ! -mtime -3 \)

You may want to execute one command on the file(s) or folder(s) found, -exec and ok (-exec with confirmation) fulfill this need:

 find ! -mtime 1000 -ok mv {} trash \;

For more complex commands, you may want to use xargs with a pipe, see http://en.wikipedia.org/wiki/Xargs.

Locate

Todo

Hard drive disk usage

df

To know how much space is available on "mounted" partitions:

 df -h # -h for human-readable size format

du

To know the size of a directory:

 du mydirectory               # lists all the content of mydirectory and sums to obtain mydirectory content size
 du -h mydirectory            # -h for human-readable size format
 du --max-depth=0 mydirectory # prints size of mydirectory 

Memory usage

To know how much RAM memory is available/used/free on your system:

 free
 free -m # displays memory in megabytes

Processes management

Ressource usage

 top # lists most processor-consuming processes with their pid

Kill

To kill a process, you can either use kill or killall commands, the first uses process' id (or pid), the latter uses process' name:

 kill 3548                # kills process for which pid is 3548
 killall this-application # kills process named this-application

Sometime, the process won't be killed, in that case, the following option could be useful:

 kill 3548 -s KILL                # kills for sure!
 killall this-application -s KILL

Permissions management

Permissions on files and folders is what makes Unix systems more secure, althought this alone cannot be a "warranty".

To change owner of a file or folder:

 chown me:mygroup myfile         # change myfile's owner to "me" and its group to "mygroup"
 chown me:mygroup mydirectory    # change mydirectory's owner to "me" and its group to "mygroup"
 chown me:mygroup mydirectory -R # change mydirectory's and its content's owner to "me" and their group to "mygroup", recursively

To change permissions modes on a file or folder:

 chmod 400 myfile               # rights become r--------
 chmod 200 myfile               # rights become -w-------
 chmod 100 myfile               # rights become --x------
 chmod 764 myfile               # rights become rwxrw--r--
 chmod u+x myfile               # adds execute mode for myfile's owner user
 chmod g+x myfile               # adds execute mode for myfile's owner group
 chmod o+x myfile               # adds execute mode for myfile's others
 chmod +x myfile                # adds execute mode for myfile's owner user, group and others
 chmod 700 mysecretdirectory -R # applies rwx------ rights to all content of mysecretdirectory, recursively

Download

To download the file at http://heanet.archive.gnewsense.org/gnewsense/cdimage/gnewsense-livecd-deltah-2.1.iso.torrent in command-line, do:

 wget http://heanet.archive.gnewsense.org/gnewsense/cdimage/gnewsense-livecd-deltah-2.1.iso.torrent

To continue an interrupted download:

 wget -c url-to-myfile

Extraction

To extract a compressed tar file (or tarball):

 tar -xzf myfile.tar.gz  # extract (-x) using gzip (-z) file (-f) "myfile.tar.gz"
 tar -xvzf myfile.tar.gz # -v: verbose
 tar -xjf myfile.tar.bz2 # extract using bzip2 (-j)

To extract a compressed gz file:

 gunzip myfile.gz

To extract a compressed bz2 file:

 bunzip myfile.bz2

Mount

To mount the partition /dev/hda2 on /mnt/hda2:

 mount /dev/hda2 /mnt/hda2
 mount /dev/hda2 /mnt/hda2 -t vfat              # if filesystem of /dev/hda2 is fat32
 mount myfile.iso /mnt/cdrom -t iso9660 -o loop # content of myfile.iso is then browsable in /mnt/cdrom

If you want to automatically mount some partitions at startup, you may be interested by /etc/fstab.

Package management

This section is specific to gNewSense and deb based GNU/Linux distributions.

Search a package

To look for a package in the distribution you are using:

 apt-cache search package

Show details on a package

 apt-cache show package

Manage packages

See also the page on apt-get and aptitude.

Available online

To install a package available for the distribution you are using:

 apt-get install package
 apt-get install package1 package2
 aptitude install package
 aptitude install package1 package2

To remove an installed program:

 apt-get remove package
 apt-get remove package1 package2
 aptitude remove package           # removes also package's dependancies which are not necessary for others
 aptitude remove package1 package2

To synchronize your system's list of packages with server's list:

 apt-get update
 aptitude update

To update packages you already installed on your system:

 apt-get upgrade
 aptitude safe-upgrade

Available offline

To install a deb package you have downloaded:

 dpkg -i package.deb

To remove a deb package you have installed:

 dpkg -r package.deb

Keyboard shortcuts

There are some useful keyboard shortcuts in command-line:

 ctrl-C       # interrupts the program which is currently running
 ctrl-D       # exits
 ctrl-L       # cleans screen
 ctrl-shift-T # opens a new tab (in terminal emulators such as gnome-terminal)

Useful links

The FSF sells the book Introduction to the Command Line, you can also read the book online for free (as in "free beer"). Finally there is a summary of command-line commands.