A shell scripting uses the Linux commands to perform a particular task. It provides loop and conditional control structures that repeat Linux commands or make decisions on which commands you want to execute. It will be very easy to learn if you already have some experience in programming (a very basic level will also work fine).
Shell Scripting provides automation, makes repetitive task, system monitoring easier to perform. Its easier to get started with it. System admins use shell scripting for routine backups and various other tasks.
A shell, by definition, is an interpretive environment within which you execute commands. It provides users with an interface and accepts human-readable commands into the system and executes those commands which can run automatically and give the program’s output. When you run the terminal, the Shell issues a command prompt (usually $), where you can type your input,(commands) which is then executed when you hit the Enter key. The output or the result is thereafter displayed on the terminal.
Types of Shell
There are different types of shells available for the linux distributions:
•BASH (Bourne Again SHell) – This is a Unix shell and command language written by Brian Fox for the GNU Project as a free software replacement for the Bourne shell. It is most widely used shell in Linux systems. It is used as default login shell in Linux systems and in macOS. You can install it on Windows OS also.
•CSH (C SHell) – This is a Unix shell created by Bill Joy while he was a graduate student at University of California, Berkeley in the late 1970s. The C shell’s syntax and usage are very similar to the C programming language.
•KSH (Korn SHell) – KornShell ( ksh ) is a Unix shell which was developed by David Korn at Bell Labs in the early 1980s and announced at USENIX on July 14, 1983. The Korn Shell also was the base for the POSIX Shell standard specifications etc.
How to write shell script
You can write shell scripts using text editors. On your Linux system, open a text editor program, open a new file to begin typing a shell script or shell programming, then give the shell permission to execute your shell script.Let us understand the steps in creating a Shell Script:
- Create a file using a vi editor(or any other editor).
- Name the file with the extension .sh .
- Start the script with #! /bin/sh (She-bang).
- Write some code .
- Save the script file.
- Make the script executable with command chmod +x .sh .
- For executing the script type bash .sh or ./.sh .
Shell scripting is the method of instructing the shell to perform some functions through the shell script. The Shell script is a computer program or an environment designed to be run by a UNIX-like Operating System, which can be easily understood and interpreted by the Unix kernel.
Shell scripting allows you to utilize the powerful capabilities of the shell and automate a lot of sequential tasks, which otherwise would require a lot of commands. Scripting is increasingly gaining popularity in today’s world, spanning from the networking domain to supercomputers. Once you learn simple bash commands, you can easily learn Python and Perl, as you will be well aware of how Linux works and what it can do.
Gaining expertise in basic administrative commands on command-line Interface (CLI) will help you automate the routine tasks and will help you save more time, whether you are a system administrator, a developer, or a Linux enthusiast.
The prompt, “$”, is called the command prompt, which is displayed by the Shell. This command prompt is the interface, on which you can write and execute your commands and programs.
The command prompt reads the first word and interprets the command. The Shell reads the command only once you press “Enter”.
Like the general variables in other programming languages, the Shell script also has variables. Variables store data or point to the location of data.
The shell allows for the creation, execution, and deletion of the variables.
The variable name can have only letters (a to z or A to Z), numbers (0 to 9), or the underscore character (_). The wrong character usage in the variable name will cause a syntax error.
Types Of Variables
There are three types of variables on a running script. They are:
•Local variables: Local variables are present in the current instance of the shell. They are set by the command prompt.
•Environment variables: These are the variables defined by the shell script. Only those required will be defined. They are available to all the child processes of the shell.
•Shell variables: These are special variables required for the proper functioning of the shell. They can be either local variables or environment variables.
Advantages of Shell Scripting
•The syntax used in shell scripting is very simple and easy to implement. The commands are exactly the same as those used directly in the CLI.
•Often, writing and executing a shell script is faster than coding and executing in an equivalent coding language.
•The program or file selection is easy in shell scripting.
•The scripting offers interactive debugging, logical sequencing, and decision-making linkage for the existing programs.
•The absence of compilation of code turns out to be an advantage for moderately small scripts.
•The interpretive nature makes it simpler to debug, by writing the debugging code into a script, which can be re-run multiple times to detect and fix the bugs.
•Automation of the frequently performed tasks like rolling logs, extracting data, etc., can be performed efficiently.
•A sequence of commands can be executed at once through a script.
•It is portable, that is, it can be deployed in any UNIX-like system, without any modifications.
Shell scripting is very useful to perform operations in Linux and other UNIX-like operating systems. It forms one of the powerful ways of programming in Linux. The scripting language is easy and syntax is not heavy on the processor.
Many programmers and tech geeks across the world prefer to work on Linux systems to code, as it offers one of the robust means of coding like shell scripting.