You fall off and scrape your knees a lot at first. With a bit more experience, you become comfortable riding them around town, but also quickly discover why most people drive cars for longer trips. Shell scripting is generally considered to be a glue language, ideal for creating small pieces of code that connect other tools together. While shell scripts can be used for more complex tasks, they are usually not the best choice. 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. If you don’t true your scripts, they wobble. 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. This chapter and the next two chapters introduce the basic concepts of shell scripting. The remaining chapters in this document provide additional breadth and depth. This document is not intended to be a complete reference on writing shell scripts, nor could it be.
It does, however, provide a good starting point for beginners first learning this black art. There are many different dialects of shell scripts, each with their own quirks, and some with their own syntax entirely. 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. 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. The C shell syntax is more comfortable to many C programmers because the syntax is somewhat similar. However, the Bourne shell syntax is significantly more flexible and thus more widely used. For this reason, this document only covers the Bourne shell syntax. The second hard lesson you will invariably learn is that each dialect of Bourne shell syntax differs slightly. This document includes only pure Bourne shell syntax and a few BASH-specific extensions. Where BASH-specific syntax is used, it is clearly noted. 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. Stay on the narrow road and your code will be portable. Some common shells are listed below, grouped by script syntax:īcsh (C shell to Bourne shell translator/emulator) #Uninstall sep quickmenu mac code# Many of these shells have more than one variation. 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.
0 kommentar(er)
