Linux shell or the terminal is the lifeline of developers to manage their computer systems and data. Things which can be done on the GUI can be done much efficiently on the terminal by using commands. One can not remember all the commands, but with regular usage, one will be familiar with them. The following guide will introduce you to some basic Linux Shell Commands required to use your Linux system efficiently.

Gnome Terminal

Below, you can see a screenshot of the Gnome terminal application. As you can see the command prompt contains the following information:

 [username@hostname directoryname]  

In our case the username is root, hostname is monitor and directory is /root(~).

A terminal and a shell:

Read the articles on Wikipedia to learn about computer terminals and the shell.

Date command:

The date command shows the current date and time.

$ date 
Tue Jan 22 10:13:44 IST 2019 

If you want to see the current date and time in UTC you can run the command as follows:

 $ date -u 

Cal command:

The cal command will display calendar in your shell, by default it displays current month.

 $ cal 
 January 2019
 Su Mo Tu We Th Fr Sa
        1  2  3  4  5
  6  7  8  9 10 11 12
 13 14 15 16 17 18 19
 20 21 22 23 24 25 26
 27 28 29 30 31

$cal Feb 2019
February 2019
 Su Mo Tu We Th Fr Sa
                 1  2
  3  4  5  6  7  8  9
 10 11 12 13 14 15 16
 17 18 19 20 21 22 23
 24 25 26 27 28

The whoami command:

This command will let you know the user account to which you are logged in on the shell.

$whoami

root

The id command:

This command returns user id, group id and groups of the current user.

$ id 
uid=0(root) gid=0(root) groups=0(root)

The pwd command:

The pwd command displays absolute path of current directory.

root@monitor:~# pwd

/root

The cd command:

This command will help you change directory on the shell. In the following example we will move to /etc/ directory.

root@monitor:~# pwd

/root

root@monitor:~# cd /etc/

root@monitor:/etc# pwd

/etc

The . directory and .. directory:

. and .. has special meaning in the Linux. i.e . means current directory and .. means parent directory.

root@monitor:/etc# cd .. 

This command will move us to the parent directory.

The ls command:

The ls command will display the files and directories inside the given directory. If you use the ls command without any argument, then it will return the output for the current directory. Here is the example:

root@monitor:/# ls
 bin   etc         key.txt  lost+found  opt   run      srv  usr
 boot  home        lib      media       proc  sbin     sys  var
 dev   initrd.img  lib64    mnt         root  scripts  tmp  vmlinuz
root@monitor:/# ls home
 ansible                 ssbackup.log  ssbackup.py-bak
 ec2-automate-backup.sh  ssbackup.py   ubuntu

In last command, we provided a path as the argument to the ls command.

The mkdir command:

Using the mkdir command you can create new directory. For example , we are creating test directory in home directory.

root@monitor:/home# mkdir test

root@monitor:/home# ls

ansible                 ssbackup.log  ssbackup.py-bak  ubuntu

ec2-automate-backup.sh  ssbackup.py   test

We can also create directories in a recursive way using -p option:

root@monitor:/home# mkdir -p  dir1/dir2/dir3

root@monitor:/home# ls

ansible  ec2-automate-backup.sh  ssbackup.py      test

dir1     ssbackup.log            ssbackup.py-bak  ubuntu

root@monitor:/home# ls dir1

dir2

root@monitor:/home# ls dir1 dir1/dir2/

dir1:

dir2

 dir1/dir2/:
 dir3

We will learn further basic commands in Part II.