However, the C shell scripting language is limited in a number of ways, many of which are hard to work around. The C shell is popular among some users as a shell for interacting with the computer because it allows simple scripts to be written more easily. For more information, see About the C Shell. Note: Because the C shell syntax is not well suited to scripting beyond a very basic level, this document does not cover C shell variants in depth. In general, with the exception of csh and tcsh, it is usually safe to assume that any modern login shell is compatible with Bourne shell syntax.
This should not be confused with the dash shell-an ash-derived shell used in some Linux distributions-whose name stands for the Debian Almquist SHell.)Īnd so on. (Oddly enough, it is not a variation of ash, the Almquist SHell, though both are Bourne shell variants. It stands for the TENEX C SHell, as some of its enhancements were inspired by the TENEX operating system. Being a public domain rewrite of AT&T's ksh, it stands for "Public Domain Korn SHell." (This is a bit of a misnomer, as a few bits are under a BSD-like open source license. Most of these variations are denoted by prefixing the name of an existing shell with additional letters that are short for whatever differentiates them from the original shell. Many of these shells have more than one variation. Some common shells are listed below, grouped by script syntax:īcsh (C shell to Bourne shell translator/emulator)
#OS X SHELL SCRIPT DOUBLE CLICK CODE#
Stay on the narrow road and your code will be portable. The terminology and subtle syntactic differences can be confusing-even a bit overwhelming at times had Dorothy in The Wizard of Oz been a programmer, you might have heard them exclaim, "BASH and ZSH and CSH, Oh My!" Fortunately, once you get the basics, things generally fall into place as long as you avoid using shell-specific features. Where BASH-specific syntax is used, it is clearly noted. This document includes only pure Bourne shell syntax and a few BASH-specific extensions. The second hard lesson you will invariably learn is that each dialect of Bourne shell syntax differs slightly. For this reason, this document only covers the Bourne shell syntax. However, the Bourne shell syntax is significantly more flexible and thus more widely used. The C shell syntax is more comfortable to many C programmers because the syntax is somewhat similar.
To that end, the first lesson you must learn before writing a shell script is that there are two fundamentally different sets of shell script syntax: the Bourne shell syntax and the C shell syntax. Because of these differences, the road to good shell scripting can be fraught with peril, leading to script failures, misbehavior, and even outright data loss. There are many different dialects of shell scripts, each with their own quirks, and some with their own syntax entirely. It does, however, provide a good starting point for beginners first learning this black art. This document is not intended to be a complete reference on writing shell scripts, nor could it be. The remaining chapters in this document provide additional breadth and depth. This chapter and the next two chapters introduce the basic concepts of shell scripting. Put another way, it is often easy to write a script, but it can be more challenging to write a script that consistently works well. If you don’t true your scripts, they wobble.
If you have ever successfully trued a bicycle wheel (or paid someone else to do so), that’s similar to learning the basics of shell scripting.
While shell scripts can be used for more complex tasks, they are usually not the best choice. Shell scripting is generally considered to be a glue language, ideal for creating small pieces of code that connect other tools together. With a bit more experience, you become comfortable riding them around town, but also quickly discover why most people drive cars for longer trips. You fall off and scrape your knees a lot at first. Writing a shell script is like riding a bike.
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