Why use the command-line?

"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)

There are many varieties of Linux, but almost all of them use similar commands that can be entered from a command-line interface 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-line interface 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 command-line terminal; they do not memorize them.

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

This page will outline a few crafty shortcuts which can make using a command-line interface easier.

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 Elevated Privileges

Most of the following commands will need to be prefaced with the sudo command. This elevates privileges to the root-user administrative level temporarily, which is necessary 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 sudo (administrative) privileges will be able to use this command. You should never use normal sudo to start graphical applications as root. (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 -rinstead.
mkdir: The mkdir command will allow you to create directories. Example: "mkdir music" will create a directory called "music".
man: The man command is used to show you the manual of other commands. Try "man man" to get the man page forman itself. See the "Man & Getting Help" section down the page for more information.
sudo: The sudo command is used to perform file operations on files that the Root User would only be allowed to change. An example would be trying to move one of your documents that another user accidentally moved to / back to yourdocuments directory. Normally, to move the file, you would type mv /mydoc.odt ~/Documents/mydoc.odt, but you are not allowed to modify files outside of your home directory. To get around this, you would type sudo mv /mydoc.odt ~/Documents/mydoc.odt. This will successfully move the file back to its correct location, provided that you are not astandard user, who has less (administrative) ability than an administrator. Be aware, though, that by using the sudocommand, you need to be extra careful. It is easier to damage your system by using the sudo command. For more information about the sudo command, click here.

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 becompiled 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/

-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

"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

$Warning /!\$ 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 orinfo page first, and try the long option --help before -h.

Searching for man files

If you aren't sure which command or application you need to use, you can try searching the man files.

man -k foo will search the man files for foo. Try "man -k nautilus" to see how this works.
- Note that this is the same as doing apropos command.
man -f foo searches only the titles of your system's man files. Try "man -f gnome", for example.
- Note that this is the same as doing whatis command.

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

Up Arrowor Ctrl + P	Scrolls through the commands you've entered previously.
Down Arrowor Ctrl + N	Takes you back to a more recent command.
Enter	When you have the command you want.
tab	A very useful feature. It autocompletes any commands or filenames, if there's only one option, or else gives you a list of options.
Ctrl + R	Searches for commands you've already typed. When you have entered a very long, complex command and need to repeat it, using this key combination and then typing a portion of the command will search through your command history. When you find it, simply press Enter.
History	The history command shows a very long list of commands that you have typed. Each command is displayed next to a number. You can type !x to execute a previously typed command from the list (replace the X with a number). If youhistory output is too long, then use history \| less for a scrollable list.

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.

Ctrl + A or Home	Moves the cursor to the start of a line.
Ctrl+ E or End	Moves the cursor to the end of a line.
Esc + B	Moves to the beginning of the previous or current word.
Ctrl + K	Deletes from the current cursor position to the end of the line.
Ctrl + U	Deletes from the start of the line to the current cursor position.
Ctrl + W	Deletes the word before the cursor.
Alt + B	Goes back one word at a time.
Alt + F	Moves forward one word at a time.
Alt + C	Capitalizes letter where cursor is and moves to end of word.

More ways to run a terminal

You can also get it with a function key

You can run more than one - 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

Starting an application, and using the Tab key

To start an application from the terminal, just type the name. Let's start gedit, and use Tab to complete the name.

First, type ged as done below

user@host:~$ ged

Press the Tab key to auto-complete the name. It should now read:

user@host:~$ gedit

Press Enter to start gedit from the terminal. Before continuing, quit gedit.

Installing applications

Installing applications from the terminal is easily done using apt-get. To search for applications, we use apt-cache. Both belong to the same program called apt.

Search for videolan:

user@host:~$ apt-cache search videolan

You should get a long list of packages related to videolan. To install vlc-plugin-jack (will allow you to use vlc with jack):

user@host:~$ sudo apt-get install vlc-plugin-jack

What is sudo?

Sudo is a command that lets' you perform other commands as 'superuser'. Installing programs is not allowed for a normal user. When using sudo, you need to use your user password to allow passing the command that follows it.

More basic commands, and starting scripts

Up and Down Arrow Keys

You already know how to use the Tab key, which saves you a lot of effort when typing. Other helpful keys are the up and downarrow keys. Pressing up will page back in history of the commands you have used. Pressing Down will page forwards.

Download a script

This script is called myscript.sh, and the only thing it does is prints some text when you execute it from the terminal. Download it into your Download folder.

Change to another directory and start the script

Now, if you downloaded the script into your Download folder in your user home directory, you could do following to start it from the terminal.

Try the ls command:

user@host:~$ ls

You should see a list of files and folders in your home directory. To change to the Downloads directory use the cd command:

user@host:~$ cd Downloads

Notice that the prompt looks different now:

user@host:~/Downloads$

Now, you could do ls again to see what is in the Downloads directory. And to start the script, you do:

user@host:~/Downloads$ ./myscript.sh

If you aren't able to start the script, it may be that it isn't set to be executable. To make the script executable, do:

user@host:~/Downloads$ chmod +x myscript.sh

And then, try again.

Finally, to get back to your home directory you can do:

user@host:~/Downloads$ cd ../

Also, just using cd without an argument will get you back to your home directory.

How to find help about different commands

Each command usually has one or two help sections. To see a shorter help section for the ls command, do:

user@host:~ ls --help

To get the more extensive manual, do:

user@host:~ man ls

To quit the manual, press q.

That's all for this short guide. Hopefully you have learned enough about using the command line to know how to follow simple tutorials and guides that involve the terminal.

Technical Knowledge Overview

Tuesday, 17 May 2016

Using The Terminal in Ubuntu Basics

Why use the command-line?

Starting a Terminal

In Unity

In GNOME

In Xfce (Xubuntu)

In KDE (Kubuntu)

In LXDE (Lubuntu)

Commands

sudo: Executing Commands with Elevated Privileges

File & Directory Commands

Running a File Within a Directory

System Information Commands

Adding A New User

Options

"Man" and getting help

Searching for man files

Other Useful Things

Prettier Manual Pages

Pasting in commands

Save on typing

Change the text

More ways to run a terminal

An extremely handy tool :: Incremental history searching

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

Starting an application, and using the Tab key

Installing applications

More basic commands, and starting scripts

Up and Down Arrow Keys

Download a script

Change to another directory and start the script

How to find help about different commands