Home
>
Software
>
Intro to UNIX Shells

Intro to UNIX Shells

A UNIX Shell is in simplest terms, a command line interpreter, that takes the users input and gives it to the Kernel. If you are familiar with DOS, you will remember the 'command.com' that file takes the users information and passes it to the operating system in a way it can be understood by the system. With DOS you only had one type of shell, but with UNIX you have a variety, each with their own abilities, pluses and minuses.

Keep in mind as you read about these shells, that though they may have major differences when they were created, that they have been updated and many features that were once only available in a single shell, may be available in other shells. This is more of a history lesson.

'sh'
The Bourne shell, named after its creator Steve Bourne is the oldest shell for most major distributions of UNIX and LINUX. Most shells today are in some fashion derived from the Bourne shell.

'csh'
The C Shell. The C shell is a great shell that has many advantages over the original Bourne shell, it was the first to introduce a history (the ability to scroll up, to view past commands). Also the C Shell as the name implies also integrates a great portion of the C programming language. If you are able to program in C, you can pretty much do it all in a shell script or from the command line, if you so desired.

'ksh'
The Korn Shell. Named after its creator David Korn. This shell is able to do most of the things both the Bourne, and C Shell can do, and improves on them. For instance, the history feature is available, plus you are able to call up the history, edit the command, and then re-run it.

'bash'
The Bourne-Again Shell. This is probably the most widely used shell to date, and is the default shell for most newer Linux distributions. Again it integrates most of the above features and improves upon them. It was developed by the Free Software Foundation.

There are many other shells out there, but chances are if you are using a UNIX style operating system, you are using one of the above mentioned shells. My personal favourite is the bash shell, which also happens to be the first one I was exposed towards, so I may be biased. However typically when shell scripting, I use the korn shell because of its programming friendly structure.

How do you know what UNIX shell I am using?

Type "ps" and then hit return at your shell prompt and you should get something similar to:

$ ps
PID TTY TIME CMD
13087 pts/1 00:00:00 bash
13121 pts/1 00:00:00 ps

The numbers under PID, TTY, TIME etc should all be different from machine to machine, and the number of lines of programs running may also. But one line you have will be probably "bash" "csh" "sh" "ksh".

Another way to check is to type the following:

grep your-user-name /etc/passwd (eg grep ken /etc/passwd)

Which will return you something along the lines of:

ken:x:501:501:Ken:/home/ken:/bin/bash

The last portion of that line is '/bin/bash' which tells you your default shell when you login.

Ken Dennis
ken.dennis@gmail.com
ken.dennis@gmail.com

Lincoln Stretch rentals Alsip ..

In The News:

Tech guru Kurt "CyberGuy" Knutsson offers solutions to fixing a personal computer that freezes up. There are a number of reasons this might be happening.

The rollout of Apple's iOS 17 brought a subtle "Rebound" notification tone that's gotten some criticism. Kurt "CyberGuy" Knutsson explains a fix.

Fitness centers and workout studios are starting to establish policies that prohibit shooting phone videos to protect people's privacy.

Stay up to date on the latest AI technology advancements and learn about the challenges and opportunities AI presents

Apple recently notified a small number of iPhone customers in 92 countries that their phones may be under attack by mercenary spyware.

An artificial intelligence-powered home security system can fire paintballs and tear gas at trespassers. The camera identifies human faces and animals.

Technology expert Kim Komando gives her tips and tricks on enhancing your user experience a smartphone and other devices you use everyday.

A new camera called NUCA uses artificial intelligence to create deepfake photos of subjects by stripping away clothing in close to real time.

The Kimberley Kube trail-ready camper has a compact but spacious design and combines luxury, functionality and ruggedness for a weekend getaway.

Stay up to date on the latest AI technology advancements and learn about the challenges and opportunities AI presents now and for the future.

Emails instructing you to reset your password for an account may be legitimate, or they may be scams. Kurt "CyberGuy" Knutsson explains.

Northrop Grumman's Manta Ray uncrewed underwater vehicle aims to revolutionize undersea missions — it glides through the ocean without human assistance.

Learn how to work Google's calendar application to streamline and organize your daily tasks from technology expert Kim Komando.

If you do not want Facebook to have automatic access to your private photos, follow our tips to protect yourself. Kurt “CyberGuy" Knutsson shows you how.

Kurt “CyberGuy" Knutsson goes into detail about Apple’s recent iOS update that allows iPhone users to instantly translate spoken language simply by using the Action Button.

Safeguarding your digital life with a reliable physical backup isn't just a precaution, it's a necessity. Kurt “CyberGuy" Knutsson provides the essential backup checklist.

Kurt “CyberGuy" Knutsson reveals how a Redditor exposed false recycling claims at their apartment, highlighting a report that only 21% of U.S. recyclables are processed.

Kurt "CyberGuy" Knutsson offers a travel toolkit featuring five technology tools to help you with booking flights and hotels for your summer vacation.

The bubble behind the clock on your iPhone can appear in different colors. Kurt "CyberGuy" Knutsson explains what each of those colors mean.

Scammers are using the power of artificial intelligence to mimic voices of people and are using the fake voices to commit crimes, like kidnappings.

Stay up to date on the latest AI technology advancements and learn about the challenges and opportunities AI presents now and for the future.

Tech guru Kurt "CyberGuy" Knutsson explains the science behind the Invisibility Shield, a 6-foot shield that makes people become invisible.

The International Olympic Committee on Friday announced plans to use AI in various Olympic aspects, including athlete identification, training and judging.

Tech guru Kurt "CyberGuy" Knutsson explains an easy trick to avoid squinting while working or surfing the web by zooming in on your personal computer.

Streaming giant Roku has recently been targeted by a pair of cyberattacks, and the company confirmed over a half million Roku accounts were compromised.