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Hello World

Type the following code into your terminal, then press Enter:

echo "Hello World"

This will produce the following output:

Hello World

File Manipulation

Files and directories (another name for folders) are at the heart of Linux, so being able to create, view, move, and delete them from the command line is very important and quite powerful. These file manipulation commands allow you to perform the same tasks that a graphical file explorer would perform.

Create an empty text file called myFile:

touch myFile

Rename myFile to myFirstFile:

mv myFile myFirstFile 

View the contents of a file:

cat myFirstFile

View the content of a file with pager (one screenful at a time):

less myFirstFile

View the first several lines of a file:

head myFirstFile

View the last several lines of a file:

tail myFirstFile

Edit a file:

vi myFirstFile

See what files are in your current working directory:

ls

Create an empty directory called myFirstDirectory:

mkdir myFirstDirectory

Create multi path directory: (creates two directories, src and myFirstDirectory)

mkdir -p src/myFirstDirectory

Move the file into the directory:

mv myFirstFile myFirstDirectory/

You can also rename the file:

user@linux-computer:~$ mv myFirstFile secondFileName

Change the current working directory to myFirstDirectory:

cd myFirstDirectory

Delete a file:

rm myFirstFile

Move into the parent directory (which is represented as ..):

cd ..

Delete an empty directory:

rmdir myFirstDirectory

Delete a non-empty directory (i.e. contains files and/or other directories):

rm -rf myFirstDirectory

Make note that when deleting directories, that you delete ./ not / that will wipe your whole filesystem.

File/Directory details

The ls command has several options that can be used together to show more information.

Details/Rights

The l option shows the file permissions, size, and last modified date. So if the root directory contained a dir called test and a file someFile the command:

user@linux-computer:~$ ls -l

Would output something like

-rw-r--r-- 1 user users   70 Jul 22 13:36 someFile.txt
drwxrwxrwx 2 user users 4096 Jul 21 07:18 test

The permissions are in format of drwxrwxrwx. The first character represents the file type d if it’s a directory - otherwise. The next three rwx are the permissions the user has over the file, the next three are the permissions the group has over the file, and the last three are the permissions everyone else has over the file.

The r of rwx stands for if a file can be read, the w represents if the file can be modified, and the x stands for if the file can be executed. If any permission isn’t granted a - will be in place of r, w, or x.

So from above user can read and modify someFile.txt but the group has only read-only rights.

To change rights you can use the chmod ### fileName command if you have sudo rights. r is represented by a value of 4, w is represented by 2, and x is represented by a 1. So if only you want to be able to modify the contents to the test directory

Owner rwx = 4+2+1 = 7
Group r-x = 4+0+1 = 5
Other r-x = 4+0+1 = 5

So the whole command is

chmod 755 test

Now doing a ls -l would show something like

drwxr-xr-x 2 user users 4096 Jul 21 07:20 test

Readable Size

Used in conjunction with the l option the h option shows file sizes that are human readable. Running

user@linux-computer:~$ ls -lh

Would output:

total 4166
-rw-r--r-- 1 user users   70 Jul 22 13:36 someFile.txt
drwxrwxrwx 2 user users 4.0K Jul 21 07:18 test

Hidden

To view hidden files use the a option. For example

user@linux-computer:~$ ls -a

Might list

.profile
someFile.txt
test

Total Directory Size

To view the size of the current directory use the s option (the h option can also be used to make the size more readable).

user@linux-computer:~$ ls -s

Outputs

total 4166
someFile.txt      test

Recursive View

Lets say test directory had a file anotherFile and you wanted to see it from the root folder, you could use the R option which would list the recursive tree.

user@linux-computer:~$ ls -R

Outputs

.:
someFile.txt    test

./test:
anotherFile

Basic Linux Utilities

Linux has a command for almost any tasks and most of them are intuitive and easily interpreted.

Getting Help in Linux

Process related information

File Management Commands

Linux uses some conventions for present and parent directories. This can be a little confusing for beginners.

Whenever you are in a terminal in Linux, you will be in what is called the current working directory. Often your command prompt will display either the full working directory, or just the last part of that directory. Your prompt could look like one of the following:

user@host ~/somedir $
user@host somedir $
user@host /home/user/somedir $

which says that your current working directory is /home/user/somedir.

In Linux .. represents the parent directory and . represents the current directory.

Therefore, if the current directory is /home/user/somedir, then cd ../somedir will not change the working directory.

The table below lists some of the most used file management commands

Directory navigation

Listing files inside a directory

File/directory create, copy and remove

File/directory permissions and groups

Useful shortcuts

Using The Terminal

The examples in this document assume that you are using a POSIX-compliant (such as bash, sh, zsh, ksh) shell.

Large portions of GNU/Linux functionality are achieved using the terminal. Most distributions of Linux include terminal emulators that allow users to interact with a shell from their desktop environment. A shell is a command-line interpreter that executes user inputted commands. Bash (Bourne Again SHell) is a common default shell among many Linux distributions and is the default shell for macOS.

These shortcuts will work if you are using Bash with the emacs keybindings (set by default):

Open terminal

• Ctrl + Alt + T or Super + T

Cursor movement

• Ctrl + A Go to the beginning of the line you are currently typing on.
• Ctrl + E Go to the end of the line you are currently typing on.
• Ctrl + XX Move between the beginning of the line and the current position of the cursor.
• Alt + F Move cursor forward one word on the current line.
• Alt + B Move cursor backward one word on the current line.
• Ctrl + F Move cursor forward one character on the current line.
• Ctrl + B Move cursor backward one character on the current line.

Text manipulation

• Ctrl + U Cut the line from the current position to the beginning of the line, adding it to the clipboard. If you are at the end of the line, cut the entire line.
• Ctrl + K Cut the line from the current position to the end of the line, adding it to the clipboard. If you are at the beginning of the line, cut the entire line.
• Ctrl + W Delete the word before the cursor, adding it to the clipboard.
• Ctrl + Y Paste the last thing from the clipboard that you cut recently (undo the last delete at the current cursor position).
• Alt + T Swap the last two words before the cursor.
• Alt + L Make lowercase from cursor to end of word.
• Alt + U Make uppercase from cursor to end of word.
• Alt + C Capitalize to end of word starting at cursor (whole word if cursor is at the beginning of word).
• Alt + D Delete to end of word starting at cursor (whole word if cursor is at the beginning of word).
• Alt + . Prints the last word written in previous command.
• Ctrl + T Swap the last two characters before the cursor.

History access

• Ctrl + R Lets you search through previously used commands.
• Ctrl + G Leave history searching mode without running a command.
• Ctrl + J Lets you copy current matched command to command line without running it, allowing you to make modifications before running the command.
• Alt + R Revert any changes to a command you’ve pulled from your history, if you’ve edited it.
• Ctrl + P Shows last executed command, i.e. walk back through the command history (Similar to up arrow).
• Ctrl + N Shows next executed command, i.e. walk forward through the command history (Similar to down arrow).

Terminal control

• Ctrl + L Clears the screen, similar to the clear command.
• Ctrl + S Stop all output to the screen. This is useful when running commands with lots of long output. But this doesn’t stop the running command.
• Ctrl + Q Resume output to the screen after stopping it with Ctrl+S.
• Ctrl + C End currently running process and return the prompt.
• Ctrl + D Log out of the current shell session, similar to the exit or logout command. In some commands, acts as End of File signal to indicate that a file end has been reached.
• Ctrl + Z Suspends (pause) currently running foreground process, which returns shell prompt. You can then use bg command allowing that process to run in the background. To again bring that process to foreground, use fg command. To view all background processes, use jobs command.
• Tab Auto-complete files and directory names.
• TabTab Shows all possibilities, when typed characters doesn’t uniquely match to a file or directory name.

Special characters

• Ctrl + H Same as Backspace.
• Ctrl + J Same as Return (historically Line Feed).
• Ctrl + M Same as Return (historically Carriage Return).
• Ctrl + I Same as Tab.
• Ctrl + G Bell Character.
• Ctrl + @ Null Character.
• Esc Deadkey equivalent to the Alt modifier.

Close Terminal

• Ctrl + Shift + W To close terminal tab.
• Ctrl + Shift + Q To close entire terminal.

Alternatively, you can switch to the vi keybindings in bash using set -o vi. Use set -o emacs to switch back to the emacs keybindings.

Searching for files by patterns in name/contents

A common and task of someone using the Linux Command Line (shell) is to search for files/directories with a certain name or containing certain text. There are 2 commands you should familiarise yourself with in order to accomplish this:

Find files by name

find /var/www -name '*.css'

This will print out the full path/filename to all files under /var/www that end in .css. Example output:

/var/www/html/text-cursor.css
/var/www/html/style.css

For more info:

man find

Find files containing text

grep font /var/www/html/style.css 

This will print all lines containing the pattern font in the specified file. Example output:

font-weight: bold;
font-family: monospace;

Another example:

grep font /var/www/html/

This doesn’t work as you’d hoped. You get:

grep: /var/www/html/: Is a directory

You need to grep recursively to make it work, using the -R option:

grep -R font /var/www/html/

Hey nice! Check out the output of this one:

/var/www/html/admin/index.php:  echo '<font color=red><b>Error: no dice</b></font><br/>';
/var/www/html/admin/index.php:  echo '<font color=red><b>Error: try again</b></font><br/>';
/var/www/html/style.css:  font-weight: bold;
/var/www/html/style.css:  font-family: monospace;

Notice that when grep is matching multiple files, it prefixes the matched lines with the filenames. You can use the -h option to get rid of that, if you want.

For more info:

man grep