Introduction to the Linux Command Line
What does it happen when you click a button with your mouse? When you click a button a command is executed and interpreted by the shell.
What is a shell?
A shell is a special program that allows the user to communicate with the kernel. It accepts specific commands and instructions and communicates them to the kernel. There are dozens of shells for Linux and the most popular are: Bash (Bourne Again shell) , ksh (Korn shell), csh (c shell), ash (Almquist shell) and Dash (Debian Almquist shell).
Some of you that are reading these shell names for the first may ask, “How can I learn all these shells?” The answer is that you don’t have to learn all because each of these shells does the same job but each of them has different syntax and built-in functions.
What shell is your Linux distribution using?
Open a terminal window and type ‘echo $SHELL’ like shown in Figure 1:
Ubuntu uses Bash shell also known as Bourne Again Shell. The dollar sign indicates the Bourne Shell. Shell commands may vary from shell to shell but Linux commands are the same for every shell and they differ between Linux distributions.
What is a Linux command?
A Linux command is an executable program which is stored in directories such as /bin and /usr/bin. A command is composed of three parts, the command itself, options and arguments. Command line is very useful and sometimes it is the only way to get something done. The best way to learn and remember commands is to practice a lot. Rome was not built in one day! Command line knowledge is a must for a good Linux user because there will be situations where a GUI is not available or it does not work properly. Command line is the right tool for the curious user who want to understand how computers work. Did you know that you can combine commands with each other in command line? Sometimes you will need to send the result of one command to another command, which can not be done in GUI. The great thing about learning Linux command line is that you can apply your knowledge about it in other Unix-like operating system like Mac OS, FreeBSD etc. You learn multiple operating systems simultaneously. Point and click with mouse is easy, but after some practice you will discover that you can make magic with the command line.