diff --git a/sources/tech/20181012 Command line quick tips- Reading files different ways.md b/sources/tech/20181012 Command line quick tips- Reading files different ways.md new file mode 100644 index 0000000000..30c82c1843 --- /dev/null +++ b/sources/tech/20181012 Command line quick tips- Reading files different ways.md @@ -0,0 +1,118 @@ +Command line quick tips: Reading files different ways +====== + +![](https://fedoramagazine.org/wp-content/uploads/2018/10/commandlinequicktips-816x345.jpg) + +Fedora is delightful to use as a graphical operating system. You can point and click your way through just about any task easily. But you’ve probably seen there is a powerful command line under the hood. To try it out in a shell, just open the Terminal application in your Fedora system. This article is one in a series that will show you some common command line utilities. + +In this installment you’ll learn how to read files in different ways. If you open a Terminal to do some work on your system, chances are good that you’ll need to read a file or two. + +### The whole enchilada + +The **cat** command is well known to terminal users. When you **cat** a file, you’re simply displaying the whole file to the screen. Really what’s happening under the hood is the file is read one line at a time, then each line is written to the screen. + +Imagine you have a file with one word per line, called myfile. To make this clear, the file will contain the word equivalent for a number on each line, like this: + +``` + + one + two + three + four + five + +``` + +So if you **cat** that file, you’ll see this output: + +``` + + $ cat myfile + one + two + three + four + five + +``` + +Nothing too surprising there, right? But here’s an interesting twist. You can also **cat** that file backward. For this, use the **tac** command. (Note that Fedora takes no blame for this debatable humor!) + +``` + + $ tac myfile + five + four + three + two + one + +``` + +The **cat** file also lets you ornament the file in different ways, in case that’s helpful. For instance, you can number lines: + +``` + + $ cat -n myfile + 1 one + 2 two + 3 three + 4 four + 5 five + +``` + +There are additional options that will show special characters and other features. To learn more, run the command **man cat** , and when done just hit **q** to exit back to the shell. + +### Picking over your food + +Often a file is too long to fit on a screen, and you may want to be able to go through it like a document. In that case, try the **less** command: + +``` + + $ less myfile + +``` + +You can use your arrow keys as well as **PgUp/PgDn** to move around the file. Again, you can use the **q** key to quit back to the shell. + +There’s actually a **more** command too, based on an older UNIX command. If it’s important to you to still see the file when you’re done, you might want to use it. The **less** command brings you back to the shell the way you left it, and clears the display of any sign of the file you looked at. + +### Just the appetizer (or dessert) + +Sometimes the output you want is just the beginning of a file. For instance, the file might be so long that when you **cat** the whole thing, the first few lines scroll past before you can see them. The **head** command will help you grab just those lines: + +``` + + $ head -n 2 myfile + one + two + +``` + +In the same way, you can use **tail** to just grab the end of a file: + +``` + + $ tail -n 3 myfile + three + four + five + +``` + +Of course these are only a few simple commands in this area. But they’ll get you started when it comes to reading files. + +-------------------------------------------------------------------------------- + +via: https://fedoramagazine.org/commandline-quick-tips-reading-files-different-ways/ + +作者:[Paul W. Frields][a] +选题:[lujun9972][b] +译者:[译者ID](https://github.com/译者ID) +校对:[校对者ID](https://github.com/校对者ID) + +本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译,[Linux中国](https://linux.cn/) 荣誉推出 + +[a]: https://fedoramagazine.org/author/pfrields/ +[b]: https://github.com/lujun9972