The shellA shell is a
command interpreter which allows the user to interact with the computer. The way things work is simple: the user types in commands, the shell interprets them and performs the tasks it was asked to do, and finally it sends the result to the standard output (which is usually the screen). For example, the output of the
ls command can be something like:
$ lsbin dev home lost+found opt sbin sys varboot etc initrd.img media proc selinux tmp vmlinuzcdrom floyd lib mnt root srv usrThis is a list of files inside the root directory. The root directory is the first location in the filesystem hierarchy, and it is represented by a slash sign:
/.
Some of the most popular shells are:
bash Bourne-Again Shell, the default shell on most Linux systems
sh Bourne Shell, an older shell which is not so widely used anymore and it has been replaced by Bash
csh C Shell, with a syntax that resembles the C programming language syntax
tcsh an improved version of the C Shell
ksh Korn Shell
dash Debian Almquist Shell
To access a shell-like application you can use, for example, GNOME Terminal (the GNOME terminal application) or Konsole (the KDE terminal application). To open either of those, press Alt+F2, and type either
gnome-terminal or
konsole in the Run dialogue that appears. You can also press Alt+Ctrl+F1 to get a shell login prompt, and you can return to the graphical interface with Alt+Ctrl+F7. Some other terminal applications include
Yakuake,
xterm or
rxvt, but I recommend to stay with the default one which comes with your distribution for now.
Here is a full article about those.
Konsole, default KDE terminal application
Bash, the default shell in most Linux distributions, including Debian and Ubuntu, is a modern implementation of the older Bourne Shell (
sh). Bash was developed by the
GNU Project, which is also responsible for most of the important command-line tools widely used on a Linux system. In fact, a more appropriate name for Linux is
GNU/Linux, since any Linux-based distribution includes the Linux kernel (the core of the operating system) and the GNU tools and utilities. On a Debian system, the default shell used by the system is specified in the
/etc/passwd file.
Basic commandsCommands in Linux are executable files which can be ran to perform tasks, like listing the files in a directory or creating and renaming files for example. Examples of frequently used commands are
ls,
pwd,
date,
cat,
less,
top and so on. The general form of Linux commands is:
command option(s) filename(s)A command may or may not have arguments. An argument (also called a parameter) can be an option or a filename. Here is a list of basic, most used commands, with the exact description specified in the manual pages:
ls list directory contents
pwd print name of current/working directory
date print or set the system date and time
mkdir make directories
rm remove files or directories
mv move (rename) files
who show who is logged on
whoami print effective userid
cat concatenate files and print on the standard output
more file perusal filter for crt viewing
less opposite of more
Standard GNU tools usually have two ways of specifying an option, the short and the long syntax, so
ls -a and
ls --all will do the same thing, list files including the ones that start with a dot (
.).
Options specified between the
[ and
] brackets are optionally, for example the synopsis
ls [OPTION]... [FILE]... tells that neither
OPTION or
FILE needs to be necessarily specified.
The
cat command can be used to read text files, and it is especially useful for small ones.
cat will display on the screen the last page of the text file(s) passed as arguments, without the ability to scroll it in order to see the rest of the file. For larger files which are longer than one page, use the
less and
more commands, or a text editor like
nano. For example, to read the
/etc/motd (message of the day) file, one can use:
$ less /etc/motdOmit the dollar sign (
$), which is the prompt in this case. A file with some text message in it should be now displayed on the screen. To navigate in a text file using
less, use the following keyboard shortcuts:
^N to go forward one line (same effect as J)
^P to go backward one line (same effect as K)
^V to go forward one page (same effect as SPACE)
Alt+V to go backward one page
To quit and return to the prompt, type
Q. In the examples above, the
^ character stands for the CONTROL character (labeled
Ctrl), so
^N means 'press Ctrl+N'. The above shortcuts are widely used on a Linux-based OS by applications like Emacs (an advanced text editor and IDE - integrated development environment), the
man command and many others. The arrow keys can also be used, by the above method is the preferred one due to the fact that it is faster, and the user doesn't have to move the fingers to the arrows then back to the typing position.
The man commandman is used to see detailed help about a command. You can use the keyboard shortcuts mentioned above to navigate through a manual page.
Type
Q to quit the manual page and return to the shell prompt. The Q character is usually used to quit most Linux command-line applications, like
more,
less,
man and many others. If you type
H while reading a manual page, a help about the command
less will be provided (
man uses the
less tool in order to format the manual pages). Those are the commands that apply in the manual page.
The cd and pwd commandsThe commands
cd, which is used to change the current directory, and
pwd, used to print the current working directory, are both
shell built-ins. This means that they are included in the Bash program rather than a standalone command (file), like
ls or
date. Some examples of shell built-ins are
cd,
echo,
read,
exit,
logout,
alias,
fg or
bg.
You can see what
cd does by changing the current working directory to a new one and see the new path using the
pwd command:
$ pwd/home/embryo$ cd /usr/share$ pwd/usr/shareYou can now type ls to see the available files in
/usr/share. As a note,
cd without any arguments changes the current directory to the home directory of the current user, located by default in
/home/username:
$ pwd/usr/share$ cd$ pwd/home/embryoControl charactersA shell uses certain key combinations to perform certain tasks. These key combinations are called
control characters. Here are examples of control characters:
^A - go to the start of line
^E - go to the end of line
^H - erase one character to the left (same effect as Backspace)
^D - erase one character to the right; it also ends the session if there is nothing to delete
^U - erase entire line
^K - erase everything to the right until the end of line
^P - bring the previous command in history
^N - bring the next command in history
^C - interrupt character: this usually terminates programs
Those are very important because they make working with the shell faster and easier. Although a little tough to learn for a beginner, they prove fast once they are learned.
Regarding
^N and
^P: for example if you type
ls, then
date and
pwd, and after that
^P, the
pwd command will be brought back and you only have to type Enter to issue it again. If you type
^P again, the
date command is brought and so on.
Regarding
^D, also called the
EOF (end-of-file) character: this key combination can also be used to tell a program that the input has ended and it can return its output. For example, you can type
wc -l, which is the command to count the lines in a text file, without providing the text file. Now you can start filling in lines and typing Enter after each line. When you're done, just type Ctrl+D and the
wc tool will return the total number of lines you entered:
$ wc -lThere is a house in New OrleansThey call the rising sunAnd it's been the ruin of many a poor boyAnd god I know I'm one4As you can see, there were 4 lines typed in.
The ls commandThe ls command is used to list directory contents. With no arguments, it returns a list of files and directories in the current directory. It also offers many arguments, so you can list more information about the existing files. For example:
ls -l use a long listing format
ls -X sort alphabetically by extension
ls -h display sizes in human readable format (transforms in KB, MB or GB when necessary); use this with the
-l switch to see the effect
ls -a list all files; this includes files starting with a dot character
You can nest arguments to obtain the desired result:
$ ls -lhXtotal 96Kdrwxr-xr-x 2 root root 4.0K 2009-03-12 16:58 bindrwxr-xr-x 3 root root 4.0K 2009-03-20 23:08 bootlrwxrwxrwx 1 root root 11 2009-02-18 18:22 cdrom -> media/cdromdrwxr-xr-x 13 root root 4.2K 2009-04-07 06:25 devdrwxr-xr-x 120 root root 12K 2009-04-07 02:18 etc...Notice that this way
ls will return the current directory contents, however you can use it to list files located in some other directory:
$ ls -lh /bintotal 4.3M-rwxr-xr-x 1 root root 685K 2008-05-12 22:02 bash-rwxr-xr-x 1 root root 121K 2007-07-14 00:52 bsd-csh-rwxr-xr-x 3 root root 26K 2008-08-05 14:19 bunzip2-rwxr-xr-x 1 root root 368K 2008-09-08 02:29 busybox-rwxr-xr-x 3 root root 26K 2008-08-05 14:19 bzcat...The . and .. filesWhen using
ls -a, you will notice two special files,
. (one dot) and
.. (two dots). These are virtual files. The single dot stands for the current working directory, while the double dot represents the parent directory of the current directory. For example if your current directory is
/home/chris/ and you want to change it to its parent
/home, you can either use
cd /home (which is the absolute path) or
cd .. (which is the relative path). Or if you want to copy, say, the file
/etc/motd in the current directory, you can use:
$ cp /etc/motd .Instead of:
$ cp /etc/motd /home/chrisThe rm, mkdir and touch commandsTo remove a file, use the rm command:
$ rm fileTo remove a directory, use:
$ rm -r directoryThe m
kdir command is used to create directories:
$ mkdir mydirtouch is a tool used to change file timestamps. That means it updates the date a file was last accessed and/or modified. Example:
$ ls -lh ubuntupocketguide-v1-1.pdf-rw-r--r-- 1 embryo embryo 2.2M 2009-01-20 21:51 ubuntupocketguide-v1-1.pdfThe file was last modified on January 20, 2009, at 21:51. To update its modification time, type:
$ touch ubuntupocketguide-v1-1.pdf$ ls -lh ubuntupocketguide-v1-1.pdf-rw-r--r-- 1 embryo embryo 2.2M 2009-04-07 16:41 ubuntupocketguide-v1-1.pdfNow, the date the file was last modified was changed to April 7, 2009, at 16:41. If the file specified as argument for touch does not exist, an empty file is created:
$ ls myfile.txtls: cannot access myfile.txt: No such file or directory$ touch myfile.txt$ file myfile.txtmyfile.txt: emptyWe used the
file command to see what what kind of file
myfile.txt is.
Getting helpOne of the most powerful ways to get help is to read the manual pages, usually available for any GNU utility and application via the
man command. These tools also have two standard arguments,
--version (or
-v) and
--help (or
-h). They return the version of the program and a brief help on how to use the respective command. You can also use
info command.
On a usual Linux system, the manual pages are located in the directory
/usr/share/man, in directory names like
man1,
man2,
man3 and so on.
$ bash --versionGNU bash, version 3.2.39(1)-release (i486-pc-linux-gnu)Copyright (C) 2007 Free Software Foundation, Inc.Shell built-insShell built-ins are commands included in the Bash program. To see the available built-ins in your Bash application, you can type
help in any shell. Some examples of built-ins include:
. (or
source) - read and execute commands from a filename
alias - define aliases (read
here how to create aliases)
bg - place each job specified as argument in the background
fg - place the job specified as argument in the foreground and make it the current task
read - read one line from the standard input
if - execute commands if the condition specified is true
while - execute commands as long as a condition is true
help - display helpful information about built-in commands
You can use the
help command to see a complete list of shell built-ins, and
help to see detailed help about each command. In order to see if a command is a standalone program or a shell built-in, you can use the
type command:
$ type cdcd is a shell builtin$ type bashbash is hashed (/bin/bash)If the specified command is an alias, the output will be something like:
$ type lsls is aliased to `ls --color=auto'Linux directory structureUsually, the standard Linux directory structure is as follows:
/bin contains essential programs for booting and maintaining the system; examples: bash, chmod, chown, cp, grep, kill, ps, rm, tar
/boot contains the Linux kernel image used to boot the system, and also the /boot/grub/menu.lst file, for configuring the GRUB boot menu
/dev special files pointing to system devices
/etc configuration files for various applications
/home contains directories for all the users a system has; examplse: /home/embryo, /home/pink
/lib contains shared libraries available for all programs throughout the system
/media mount points for devices like hard disks or optical drives
/mnt used for mount points like external filesystems
/opt additional applications go here
/proc virtual files which provide information about the system; try cat /proc/cpuinfo for example
/root home for the super user (root)
/tmp temporary files are stored here
/sbin programs for system administration, generally used by root
/usr contains almost all the programs which are not located in /bin or /sbin, documentation, manual pages, icons etc
/var files like logs, emails
Using tar, gzip and bzip2tar is a tool which creates archives known as tarfiles, while
gzip is a compressing tool which uses an advanced compression algorithm.
bzip2 is an advanced compression tool which takes more time to compress/uncompress files but offers a better compression rate, which results in smaller files.
bzip2 is used especially to save disk space and bandwidth.
To uncompress a
.tar.gz file you would issue a command like:
tar -xzf archive.tar.gzx stands for extract
z specifies that the compressed file is a gzip file
f stands for the filename
To uncompress a
.tar.bz2 file you can use:
tar -xjf archive.tar.bz2To create a
.tar.gz file from a directory, you can use:
tar -czf my_archive.tar.gz directory_nameThis will create the compressed file
my_archive.tar.gz from the contents of
directory_name, which will be the root directory.
More Linux commandswhoThe command
who is used to show who is logged on, the number of the tty (teletype terminal) or display they are using, and the date and time they logged in:
$ whoembryo tty1 2009-04-07 17:08embryo :0 2009-04-06 23:30uptimeuptime will show how long the system has been running:
$ uptime 17:09:03 up 17:39, 2 users, load average: 0.14, 0.17, 0.11unameThis command is used to print system information:
$ uname -aLinux debian 2.6.26-1-686 #1 SMP Fri Mar 13 18:08:45 UTC 2009 i686 GNU/LinuxechoThis built-in will display a line of text to the screen:
$ echo 'Hello, world!'Hello, world!$ echo $PATH/home/embryo/bin:/usr/local/bin:/usr/bin:/bin:/usr/gamesSearch for commandsIn order to see the path in which a command is located, you can use the
whereis command, which will search in all the standard locations:
$ whereis bashbash: /bin/bash /etc/bash.bashrc /usr/share/man/man1/bash.1.gzNotice that
whereis will not look into non-standard paths (e.g.
/home/user/bin), instead, you can use the
which command for that:
$ which q3ut4.bash/home/embryo/bin/q3ut4.bashWhen you type in a command like
uptime or
uname, Bash searches for it in the directories in your
$PATH variable (see
echo $PATH), and it executes the first one it finds in that order. Aliases have priority.
Additional resourcesThere is a huge number of tutorials for Linux CLI, but I'd like to recommend two particular ones, specially created for beginners:
TuxFiles.org - Tutorials for Linux newbies
LinuxCommand.org - An introduction to Linux command-line and basic scripting for beginners
Do you have any suggestions or corrections for this tutorial? Please feel free to discuss in the comments section below.
This is a later, revised version of the tutorial which I initially published here.
Updated: April 9, 2009
Source URL: http://ashesgarrett.blogspot.com/search/label/beginnerVisit ashes garrett for Daily Updated Hairstyles Collection
Finch is a powerful text user interface instant messaging client based on libpurple, and it comes included in the Pidgin source, the popular GNOME IM client. Finch supports various protocols, including AIM, ICQ, MSN, Yahoo and IRC.
Source URL: http://ashesgarrett.blogspot.com/search/label/beginner
