Why use the terminal?

"Under Linux there are GUIs (graphical user interfaces), where you can point and click and drag, and hopefully get work done without first reading lots of documentation. The traditional Unix environment is a CLI (command line interface), where you type commands to tell the computer what to do. That is faster and more powerful, but requires finding out what the commands are."
-- from man intro(1)

This page gives an introduction to using the command-line interface terminal, from now on abbreviated to the terminal. There are many varieties of Linux, but almost all of them use similar commands that can be entered from the terminal.

There are also many graphical user interfaces (GUIs), but each of them works differently and there is little standardization between them. Experienced users who work with many different Linux distributions therefore find it easier to learn commands that can be used in all varieties of Ubuntu and, indeed, in other Linux distributions as well.

For the novice, commands can appear daunting:

sudo gobbledegook blah_blah -w -t -h --long-switch aWkward/ComBinationOf/mixedCase/underscores_strokes/and.dots

However, it is important to note that even experienced users often cut and paste commands (from a guide or manual) into the terminal; they do not memorize them.

It is important, of course, to know how to use the terminal - and anyone who can manage typing, backspacing, and cutting and pasting will be able to use the terminal (it is not more difficult than that).

Starting a terminal

In Unity

Unity is the default desktop environment used as of 11.04. Where systems are not ready for Unity they revert to GNOME which is also used in previous releases such as Ubuntu 10.04 LTS (Lucid), see next sub-section.

The easiest way to open the terminal is to use the 'search' function on the dash. Or you can click on the 'More Apps' button, click on the 'See more results' by the installed section, and find it in that list of applications. A third way, available after you click on the 'More Apps' button, is to go to the search bar, and see that the far right end of it says 'All Applications'. You then click on that, and you'll see the full list. Then you can go to Accessories -> Terminal after that. So, the methods in Unity are:

Dash -> Search for Terminal

Dash -> More Apps -> 'See More Results' -> Terminal

Dash -> More Apps -> Accessories -> Terminal

Keyboard Shortcut: Ctrl + Alt + T

In GNOME

GNOME is the classic desktop environment for Ubuntu 11.04 (Natty) and is the default desktop environment in earlier releases, such as Ubuntu 10.04 LTS (Lucid).

Applications menu -> Accessories -> Terminal.

Keyboard Shortcut: Ctrl + Alt + T

In Xfce (Xubuntu)

Applications menu -> System -> Terminal.

Keyboard Shortcut: Super + T

Keyboard Shortcut: Ctrl + Alt + T

In KDE (Kubuntu)

KMenu -> System -> Terminal Program (Konsole).

In LXDE (Lubuntu)

Menu -> Accessories -> LXTerminal.

Keyboard Shortcut: Ctrl + Alt + T

Commands

sudo: Executing Commands with Administrative Privileges

The sudo command executes a command with administrative privileges (root-user administrative level), which is necessary, for example, when working with directories or files not owned by your user account. When using sudo you will be prompted for your password. Only users with administrative privileges are allowed to use sudo.

Be careful when executing commands with administrative privileges - you might damage your system! You should never use normal sudo to start graphical applications with administrative privileges. Please see RootSudo for more information on using sudo correctly.

File & Directory Commands

• The tilde (~) symbol stands for your home directory. If you are user, then the tilde (~) stands for /home/user

• pwd: The pwd command will allow you to know in which directory you're located (pwd stands for "print working directory"). Example: "pwd" in the Desktop directory will show "~/Desktop". Note that the GNOME Terminal also displays this information in the title bar of its window. A useful gnemonic is "present working directory."

• ls: The ls command will show you ('list') the files in your current directory. Used with certain options, you can see sizes of files, when files were made, and permissions of files. Example: "ls ~" will show you the files that are in your home directory.

• cd: The cd command will allow you to change directories. When you open a terminal you will be in your home directory. To move around the file system you will use cd. Examples:

  • To navigate into the root directory, use "cd /"

  • To navigate to your home directory, use "cd" or "cd ~"

  • To navigate up one directory level, use "cd .."

  • To navigate to the previous directory (or back), use "cd -"

  • To navigate through multiple levels of directory at once, specify the full directory path that you want to go to. For example, use, "cd /var/www" to go directly to the /www subdirectory of /var/. As another example, "cd ~/Desktop" will move you to the Desktop subdirectory inside your home directory.

• cp: The cp command will make a copy of a file for you. Example: "cp file foo" will make an exact copy of "file" and name it "foo", but the file "file" will still be there. If you are copying a directory, you must use "cp -r directory foo" (copy recursively). (To understand what "recursively" means, think of it this way: to copy the directory and all its files and subdirectories and all their files and subdirectories of the subdirectories and all their files, and on and on, "recursively")

• mv: The mv command will move a file to a different location or will rename a file. Examples are as follows: "mv file foo" will rename the file "file" to "foo". "mv foo ~/Desktop" will move the file "foo" to your Desktop directory, but it will not rename it. You must specify a new file name to rename a file.

  • To save on typing, you can substitute '~' in place of the home directory.

  • Note that if you are using mv with sudo you can use the ~ shortcut, because the terminal expands the ~ to your home directory. However, when you open a root shell with sudo -i or sudo -s, ~ will refer to the root account's home directory, not your own.

• rm: Use this command to remove or delete a file in your directory.

• rmdir: The rmdir command will delete an empty directory. To delete a directory and all of its contents recursively, use rm -r instead.

• mkdir: The mkdir command will allow you to create directories. Example: "mkdir music" will create a directory called "music".

Here is an example of when it would be necessary to execute a command with administrative privileges. Let's suppose that another user has accidentally moved one of your documents from your Documents directory to the root directory. Normally, to move the document back, you would type mv /mydoc.odt ~/Documents/mydoc.odt, but by default you are not allowed to modify files outside your home directory. To get around this, you would type sudo mv /mydoc.odt ~/Documents/mydoc.odt. This will successfully move the document back to its correct location, provided that you have administrative privileges.

Running a File Within a Directory

So you've decided to run a file using the command-line? Well... there's a command for that too!

./filename.extension

After navigating to the file's directory, this command will enable any Ubuntu user to run files compiled via GCC or any other programming language. Although the example above indicates a file name extension, please notice that, differently from some other operating systems, Ubuntu (and other Linux-based systems) do not care about file extensions (they can be anything, or nothing). Keep in mind that the 'extension' will vary depending upon the language the source code is written in. Also, it is not possible, for compiled languages (like C and C++) to run the source code directly -- the file must be compiled first, which means it will be translated from a human-readable programming language to something the computer can understand. Some possible extensions: ".c" for C source, ".cpp" for C++, ".rb" for Ruby, ".py" for Python, etc. Also, remember that (in the case of interpreted languages like Ruby & Python) you must have a version of that language installed on Ubuntu before trying to run files written with it.

Finally, the file will only be executed if the file permissions are correct -- please see the FilePermissions help page for details.

System Information Commands

df: The df command displays filesystem disk space usage for all mounted partitions. "df -h" is probably the most useful - it uses megabytes (M) and gigabytes (G) instead of blocks to report. (-h means "human-readable")

du: The du command displays the disk usage for a directory. It can either display the space used for all subdirectories or the total for the directory you run it on. Example:

user@users-desktop:~$ du /media/floppy
1032    /media/floppy/files
1036    /media/floppy/
user@users-desktop:~$ du -sh /media/floppy
1.1M    /media/floppy/

In the above example -s means "Summary" and -h means "Human Readable".

free: The free command displays the amount of free and used memory in the system. "free -m" will give the information using megabytes, which is probably most useful for current computers.

top: The top ('table of processes') command displays information on your Linux system, running processes and system resources, including CPU, RAM & swap usage and total number of tasks being run. To exit top, press "q".

uname -a: The uname command with the -a option prints all system information, including machine name, kernel name & version, and a few other details. Most useful for checking which kernel you're using.

lsb_release -a: The lsb_release command with the -a option prints version information for the Linux release you're running, for example:

user@computer:~$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 11.10
Release:        11.10
Codename:       oneiric

ip addr reports on your system's network interfaces.

Adding A New User

The "adduser newuser" command will create a new general user called "newuser" on your system, and to assign a password for the newuser account use "passwd newuser".

Options

The default behaviour for a command may usually be modified by adding a --option to the command. The ls command for example has an -s option so that "ls -s" will include file sizes in the listing. There is also a -h option to get those sizes in a "human readable" format.

Options can be grouped in clusters so "ls -sh" is exactly the same command as "ls -s -h". Most options have a long version, prefixed with two dashes instead of one, so even "ls --size --human-readable" is the same command.

"Man" and getting help

man command, info command and command --help are the most important tools at the command line.

Nearly every command and application in Linux will have a man (manual) file, so finding them is as simple as typing "man "command"" to bring up a longer manual entry for the specified command. For example, "man mv" will bring up the mv (move) manual.

Move up and down the man file with the arrow keys, and quit back to the command prompt with "q".

"man man" will bring up the manual entry for the man command, which is a good place to start!

"man intro" is especially useful - it displays the "Introduction to user commands" which is a well-written, fairly brief introduction to the Linux command line.

There are also info pages, which are generally more in-depth than man pages. Try "info info" for the introduction to info pages.

Some software developers prefer info to man (for instance, GNU developers), so if you find a very widely used command or app that doesn't have a man page, it's worth checking for an info page.

Virtually all commands understand the -h (or --help) option which will produce a short usage description of the command and it's options, then exit back to the command prompt. Try "man -h" or "man --help" to see this in action.

Caveat: It's possible (but rare) that a program doesn't understand the -h option to mean help. For this reason, check for a man or info page first, and try the long option --help before -h.

Searching the manual pages

If you aren't sure which command or application you need to use, you can try searching the manual pages. Each manual page has a name and a short description.

To search the names for <string> enter:

whatis -r <string>

For example, whatis -r cpy will list manual pages whose names contain cpy. The output from whatis -r cpy will in part depend on your system - but might be as follows:

memccpy (3)          - copy memory area
memcpy (3)           - copy memory area
mempcpy (3)          - copy memory area
[some lines removed]
wcsncpy (3)          - copy a fixed-size string of wide characters
wmemcpy (3)          - copy an array of wide-characters
wmempcpy (3)         - copy memory area

To search the names or descriptions for <string> enter:

apropos -r <string>

For example, apropos -r "copy files" will list manual pages whose names or descriptions contain copy files. The output from apropos -r "copy files" will in part depend on your system - but might be as follows:

cp (1)               - copy files and directories
cpio (1)             - copy files to and from archives
gvfs-copy (1)        - Copy files
gvfs-move (1)        - Copy files
install (1)          - copy files and set attributes

Other Useful Things

Prettier Manual Pages

Users who have Konqueror installed will be pleased to find they can read and search man pages in a web browser context, prettified with their chosen desktop fonts and a little colour, by visiting man:/command in Konqueror's address bar. Some people might find this lightens the load if there's lots of documentation to read/search.

Pasting in commands

Often, you will be referred to instructions that require commands to be pasted into the terminal. You might be wondering why the text you've copied from a web page using Ctrl + C won't paste in with ctrl+V. Surely you don't have to type in all those nasty commands and filenames? Relax. ctrl+shift+V pastes into a GNOME terminal; you can also do middle button click on your mouse (both buttons simultaneously on a two-button mouse) or right click and select Paste from the menu. However, if you want to avoid the mouse and yet paste it, use "Shift + Insert", to paste the command. If you have to copy it from another terminal / webpage, you can use "Ctrl + Insert" to copy.

Save on typing

• Example: you ran history and found you want to use command 1967. Simply enter

!1967

Change the text

The mouse won't work. Use the left/right arrow keys to move around the line.

When the cursor is where you want it in the line, typing inserts text - ie it doesn't overtype what's already there.

More ways to run a terminal

You can set your own keyboard shortcut to run a terminal. See KeyboardShortcuts for details of keyboard shortcuts.

You can run more than terminal - in tabs or separate windows.

You can also install guake (GNOME), tilda (XFCE / LXDE/Mate) or yakuake (KDE) and have a terminal which appears and hides on shortcut key. This can be particularly useful if you use terminal a lot. Drop down terminals can make things a lot easier if you are trying to run a desktop enviroment with a non defualt window manager and something goes wrong drop down terminals can run the orginal window manager --replace to restore a previous option to make things much less painful.

An extremely handy tool :: Incremental history searching

In terminal enter:

gedit  ~/.inputrc

Then copy paste and save:

"\e[A": history-search-backward
"\e[B": history-search-forward
"\e[C": forward-char
"\e[D": backward-char

From now on, and many agree this is the most useful terminal tool, it saves you a lot of writing/memorizing...

All you need to do to find a previous command is to enter say the first two or three letters and upward arrow will take you there quickly:

Say I want:

for f in *.mid ; do timidity "$f"; done

All I need to do is enter:

fo

And hit upward arrow command will soon appear.

How to create upsidedown and/or reverse text with your terminal

If you wish or need to ever flip text upside down [vertical flip] "uʍop ǝpısdn ʇxǝʇ dıʃɟ" or/and create reverse text here is a terminal way to achieve this.

Copy/paste and save the following as flip.pl in your home folder (thanks to Lars Noodén for script).

#!/usr/bin/perl

use strict;
use warnings;
use utf8;

binmode(STDOUT, ":utf8");

my %flipTable = (
    "a" => "\x{0250}",
    "b" => "q",
    "c" => "\x{0254}", 
    "d" => "p",
    "e" => "\x{01DD}",
    "f" => "\x{025F}", 
    "g" => "\x{0183}",
    "h" => "\x{0265}",
    "i" => "\x{0131}", 
    "j" => "\x{027E}",
    "k" => "\x{029E}",
    "l" => "|",
    "m" => "\x{026F}",
    "n" => "u",
    "o" => "o",
    "p" => "d",
    "q" => "b",
    "r" => "\x{0279}",
    "s" => "s",
    "t" => "\x{0287}",
    "u" => "n",
    "v" => "\x{028C}",
    "w" => "\x{028D}",
    "x" => "x",
    "y" => "\x{028E}",
    "z" => "z",
    "A" => "\x{0250}",
    "B" => "q",
    "C" => "\x{0254}", 
    "D" => "p",
    "E" => "\x{01DD}",
    "F" => "\x{025F}", 
    "G" => "\x{0183}",
    "H" => "\x{0265}",
    "I" => "\x{0131}", 
    "J" => "\x{027E}",
    "K" => "\x{029E}",
    "L" => "|",
    "M" => "\x{026F}",
    "N" => "u",
    "O" => "o",
    "P" => "d",
    "Q" => "b",
    "R" => "\x{0279}",
    "S" => "s",
    "T" => "\x{0287}",
    "U" => "n",
    "V" => "\x{028C}",
    "W" => "\x{028D}",
    "X" => "x",
    "Y" => "\x{028E}",
    "Z" => "z",
    "." => "\x{02D9}",
    "[" => "]",
    "'" => ",",
    "," => "'",
    "(" => ")",
    "{" => "}",
    "?" => "\x{00BF}", 
    "!" => "\x{00A1}",
    "\"" => ",",
    "<" => ">",
    "_" => "\x{203E}",
    ";" => "\x{061B}",
    "\x{203F}" => "\x{2040}",
    "\x{2045}" => "\x{2046}",
    "\x{2234}" => "\x{2235}",
    "\r" => "\n",
    " " => " "
);

while ( <> ) {
    my $string = reverse( $_ );
    while ($string =~ /(.)/g) {
        print $flipTable{$1};
    }
    print qq(\n);
}

Then to set it up:

sudo mv flip.pl /bin/
cd /bin/
sudo chown yourusername flip.pl && sudo chmod +x flip.pl

Then open terminal and enter:

flip.pl

else

perl /bin/flip.pl

Write what you want and hit return

Copy and paste wherever you want text document or Internet forum, etc...

• ɹǝʇuǝ puɐ ʇuɐʍ noʎ ʇɐɥʍ ǝʇıɹʍ ˙˙˙ɔʇǝ ɯnɹoɟ ʇǝuɹǝʇuı ɹo ʇuǝɯnɔop ʇxǝʇ ʇuɐʍ noʎ ɹǝʌǝɹǝɥʍ ǝʇsɐd puɐ ʎdoɔ

==================

If you want to reverse back to front, write your text in a text editor and save as mytext to the home folder.

Then enter:

rev mytext

Copy and paste the result, tluser eht etsap dna ypoc.

And of course you can combine both for truly cryptic results, ɔodʎ ɐup dɐsʇǝ ʇɥǝ ɹǝsnʃʇ

More Information

Within the Community Help Wiki:

• AptGetHowto - installing packages.

• Commandline Repository Editing - adding repositories.

• grep Howto - grep is a powerful command line search tool.

• find Howto - locating files.

• CommandlineHowto - another introduction to the terminal.

• HowToReadline - more advanced customization.

Detailed tutorials on the Linux command line:

• http://linuxtutorial.todolistme.net - "Here you will learn the Linux command line (Bash) with our 13 part beginners tutorial ...".

• http://mywiki.wooledge.org/BashGuide - "This guide aims to aid people interested in learning to work with BASH. It aspires to teach good practice techniques for using BASH, and writing simple scripts".

• http://linuxcommand.org/ - Learning the shell and writing shell scripts.

• http://linuxsurvival.com/index.php - "Linux Survival is a free tutorial designed for people who have little or no experience with the Linux operating system".

• http://www.ss64.com/bash/ - "An A-Z Index of the Bash command line for Linux".

• http://tinyurl.com/ycyg4mk - "Top 3 Sites to Help You Become a Linux Command Line Master".

CategoryCommandLine