Getting started with GNU/Linux

                    Getting started with GNU/Linux

 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.
Tab Tab 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.

 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
       Command                                                                       Utility

pwd    Get the full path of the current working directory.
cd -      Navigate to the last directory you were working in.
cd ~ or just cd Navigate to the current user's home directory.
cd ..    Go to the parent directory of current directory (mind the space between cd and ..)

Listing files inside a directory
            Command                                                                 Utility

ls -l List the files and directories in the current directory in long (table) format (It is recommended to use -l with ls for better readability).
ls -ld dir-name List information about the directory dir-name instead of its contents.
ls -a List all the files including the hidden ones (File names starting with a . are hidden files in Linux).
ls -F Appends a symbol at the end of a file name to indicate its type (* means executable, / means directory, @ means symbolic link, = means socket, | means named pipe, > means door).
ls -lt List the files sorted by last modified time with most recently modified files showing at the top (remember -l option provides the long format which has better readability).
ls -lh List the file sizes in human readable format.
ls -lR Shows all subdirectories recursively.
tree Will generate a tree representation of the file system starting from the current directory.

File/directory create, copy and remove
                Command                                                             Utility

cp -p source destination  : Will copy the file from source to destination. -p stands for preservation. It preserves the original attributes of file while copying like file owner, timestamp, group, permissions etc.

cp -R source_dir
destination_dir       : Will copy source directory to specified destination recursively.

mv file1 file2  : In Linux there is no rename command as such. Hence mv moves/renames the file1 to file2.

rm -i filename   : Asks you before every file removal for confirmation. IF YOU ARE A NEW USER TO LINUX COMMAND LINE, YOU SHOULD ALWAYS USE rm -i. You can specify multiple files.

rm -R dir-name  : Will remove the directory dir-name recursively.

rm -rf dir-name  : Will remove the directory dir recursively, ignoring non-existent files and will never prompt for anything. BE CAREFUL USING THIS COMMAND! You can specify multiple directories.

rmdir dir-name :  Will remove the directory dir-name, if it's empty. This command can only remove empty directories.

mkdir dir-name      : Create a directory dir-name.

mkdir -p dir-name/dir-name : Create a directory hierarchy. Create parent directories as needed, if they don't exist. You can specify multiple directories.

touch  filename : Create a file filename, if it doesn't exist, otherwise change the timestamp of the file to current time.

File/directory permissions and groups
              Command                                                             Utility

chmod <specification> filename : Change the file permissions. Specifications = u user, g group, o other, + add permission, - remove, r read, w write,x execute.

chmod -R <specification> dir- name : Change the permissions of a directory recursively. To change permission of a directory and everything within that directory, use this command.

chmod go=+r myfile : Add read permission for the owner and the group.

chmod a +rwx myfile : Allow all users to read, write or execute myfile.

chmod go -r myfile : Remove read permission from the group and others.

chown owner1 filename : Change ownership of a file to user owner1.

chgrp grp_owner filename :  Change primary group ownership of file filename to group  grp_owner.

chgrp -R grp_owner dir-name : Change primary group ownership of directory dir-name to group grp_owner recursively. To change group ownership of a directory and everything within that directory, use this command.