In Tcsh, however, you use the keyword set for variables: $ set foo=bar For instance, in Bash and Zsh and Ash and Ksh, you set variables with an "equals" declaration: $ foo=bar The noticeable difference between shells is syntax. That means that when you're using a shell, your default view looks something like this: A common symbol is a dollar sign ( $), but it could also be a percent sign ( %), an angle-bracket ( >), an octothorpe ( #), or something else entirely. Some people call the shell prompt a command line, which is indeed descriptive: a prompt indicates a line into which you can type a command.Ī prompt is some symbol to let you know that the shell is awaiting your instructions. When you access a shell, you get a prompt. Microsoft's Powershell is an open source. Ash and Dash aim to be lightweight and fast, making them ideal for embedded systems and for minimal environments. Tcsh and Ksh are reliable old favorites from early UNIX, with strict POSIX compliance. The most popular is (GNU) Bash, but Zsh and Fish are popular Bash alternatives. When thinking about a shell, it's helpful to think of a specific one, and there are plenty to choose from. The shell is an abstract concept for many people. That makes it the most direct way to instruct a computer about what you want it to do next, so learning the shell is an invaluable tactic of power users. Even in modern computing, a shell is the lowest level of interaction you can have with your computer. The shell transformed computers from an appliance into a power tool that could change its function on demand. The important thing to understand about a shell is that it marked a new age for computing. The shell is the part that a user interacts with, while the requests for computing power is managed by the kernel. There are different accounts on why the term "shell" was chosen, but a believable and satisfying explanation is that the shell interface surrounds the kernel just as a nutshell surrounds a nut. So they developed something they called a shell. Once computers advanced, though, some scientists recognized that programming a computer for one purpose each time it booted was inefficient and, with advances in technology, under-powered. If you wanted to process two jobs at once, you got a second computer. The concept of running a background job, or two applications at once, was unimaginable. Very early computers did even less than this in their idle state, and each program that an early computer ran was essentially its sole purpose for existing, at least while that program (in the form of punch cards) was being executed. Hardware drivers, orchestrated by the kernel, keep fans active to prevent overheating, disk space is monitored, RAM states managed, new devices are detected, and so on. The most basic set of instructions for a computer keeps it powered on. Some are very simple, and others are very complex, depending on the needs of the device it's running. There are specialized kernels for all manner of computational devices. There are many different kernels out there: long ago, there was a Unix kernel, a Sun kernel, a BSD kernel, and later there came the Linux kernel, the Hurd kernel, a Mach kernel, and an NT kernel.Īnd that's not all of them. When a computer boots up, a kernel recognizes its own physical hardware and enables each component to talk with one another.
This article guides you through the terminology of Linux text-based interfaces. They're definitely all related, but there are nuances to each that have important implications. If you're exploring Linux or Unix, you might hear the terms terminal, command line, shell, and console, and you may justifiably be confused about which is which and whether they're the same thing.
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Advanced Linux Commands Cheat Sheet for Developers.
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