A detailed explanation of the usage of Linux redirection

We usually need to copy sticker data, if you open the file to copy sticking operation, then there is tedious, then can you save these steps?

Of course, redirection is an efficient method that does not require a lot of mouse and keyboard manipulation to transfer data. R edirects can be divided into input redirects and output redirects. Because all programs have inputs or outputs, redirection of inputs and outputs comes with functionality in any programming or scripting language.

Redirection is bound to occur whenever you interact with your computer. L earning to use redirection not only allows you to interact better with your computer, but also increases your productivity. Let's take a look at common usage of redirection in Linux systems:

The data flow in Linux

When it comes to Linux redirection, we have to mention the following three streams:

• Input information is read from stdin (standard input, usually keyboard or mouse).

• The output information is output to stdout (standard output, a text file, or data stream).

• The error message is output to stderr

Knowing the existence of these data streams gives you more control over where your data flows when you use Shell

In Linux systems, standard inputs, standard outputs, and standard errors exist as files. You can see them in the /dev directory:

$ ls /dev/std* /dev/stderr /dev/stdin /dev/stdout

Redirect the output

In Linux system, the redirect output is represented by the > character. For example, redirect the output of the ls command to a file:

$ ls > list.txt

After you execute the above command, the output information for the ls command is not displayed on the screen because the output information has been redirected to list.txt file.

In addition, redirection has many uses, it can also be used to copy the contents of a file, and not limited to copying text files, binary files can also be copied:

$ cat image.png > picture.png

If you want to copy the contents of one file to the end of another, simply replace > character with >> string, like this:

$ cat lxlinux >> alvin

Redirect the input

In contrast to redirecting the output, the redirect input uses < character.

Input redirection redirects input information to the command for use as an argument. This feature may be less useful, but it comes in handy when the command requires a list of parameters that exist in a file and then you want to quickly copy and paste them from the file to the terminal.

For example, package.list records a list of packages that you need to install, and if you want to install all packages quickly, you can install all the packages in package.list at once by executing the following command:

$ sudo dnf install $(<package.list)

The common uses for input redirection are Here-document and Here-string

Here-doc redirects the input block of text to the standard input stream until a special file end tag is encountered (the file end marker can be any unique string, but most people use EOF by default).

You can try entering the following command at the terminal (until the end of the second EOF string):

$ cat << EOF

alvin lxlinux.net EOF

The expected output should look like this:

alvin lxlinux.net

Here-doc is a common technique used by Bash script writers to dump multiple lines of text onto a file or screen.

Here-string is similar to Here-doc but it has only one string, or a few strings enclosed in quotation marks:

$ cat <<< alvin alvin $ cat <<< "alvin lxlinux.net" alvin lxlinux.net

Redirect the error message

The error message enters the stream called stderr by default and can be redirected using 2> For example, redirect an error message to a file named output.log

$ ls /nope 2> output.log

Redirect the data to /dev/null

Just like standard inputs, standard outputs, and standard errors, in Linux file system, there is an empty file corresponding to it, called null which is placed in the /dev directory. For ease of reading, slashes are often omitted and read directly as dev null

/dev/null does not save data, and the data written to /dev/null is eventually lost as if it were thrown into the void air. T herefore, you can use redirection to deliver unwanted data to /dev/null For example, the output of find command is often lengthy, and errors with conflicting permissions are often reported when searching for files, such as this:

$ find ~ -type f /home/seth/actual.file find: /home/seth/foggy': Permission denied find: /home/seth/groggy': Permission denied find: `/home/seth/soggy': Permission denied /home/seth/zzz.file

At this point, you can redirect the error message to /dev/null to filter out unnecessary information, like this:

$ find ~ -type f 2> /dev/null /home/seth/actual.file /home/seth/zzz.file

Make good use of redirection

In Bash redirection is an efficient way to transfer data. Y ou may not always use redirection, but learning how to use redirection saves you a lot of unnecessary copy-and-paste operations when you need them, and therefore saves you a lot of time working with the mouse and keyboard. Please don't stick to copy and paste, using redirection can improve your productivity, isn't it?

The above is about Linux system redirection explanation, I hope to help you work, want to learn more Linux knowledge students can look at the tutorial:

Linux tutorial: https://www.w3cschool.cn/linux/

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