The Linux command line interface provides a wealth of text processing tools, one of the most powerful tools is the sed command. sed is the abbreviation of Stream EDitor, a multi-functional tool that allows complex processing of text files and streams.

What is Sed?

sed is a non-interactive text editor that operates pipe input or text files. By providing directives, you can let it modify and process text in a file or stream. The most common use cases sed include selecting text, replacing text, modifying original files, adding lines to text, or removing lines from text. It can be used from the command line in Bash and other command line shells.

Sed command syntax

The syntax of the sed command contains three main parts:

1. Options: The output of these control commands.
2. Script: This contains a list of commands to run.
3. Input file: This is the file you are using the sed command.

If there is no file name, the script will operate on the standard input data. You can also run the sed command without using any options. The basic syntax is as follows:

sed 選項[腳本] [輸入文件名]

Comparison between Sed and Awk

sed is not the only text processing tool in the Linux ecosystem. Another powerful utility is awk . While both deal with text, they have some key differences:

• sed is good at parsing and converting text in a simple and simple language, making it simple, limited but easy to use.
• awk , on the other hand, is a tool for text processing and writing powerful programs that appear in statement form. It is more complex, versatile and more powerful than sed , but also more complex.

Explore Sed with examples

Let's dig into how sed works with some practical examples. For all these examples, suppose we have a file named ik.txt . Note that sed does not change the original file by default. All changes will be displayed in the output, but the original file will remain the same.

One of the most common operations in text replacement sed is text replacement. This is done using the s command. For example, to replace the first instance of schema abc with another schema def , use:

sed s/abc/def/ ik.txt

Here, the first instance of abc in each line will be replaced by def . If you want to replace the third instance of the pattern, you can use:

sed s/abc/z/3 ik.txt

Global Replacement In global replacement, all instances of the pattern are replaced. This is done by appending g to the replacement command. To replace all abc instances with XYZ , use:

sed s/abc/XYZ/g ik.txt

You can also start global replacement with the nth instance of the pattern by using /ng . For example, to replace all abc instances with XYZ starting from the third instance, use:

sed s/abc/XYZ/3g ik.txt

In short, the sed command in Linux is a powerful stream editor that can perform multiple operations on text files and streams. It does not provide an interactive interface, but operates pipeline input or text files based on the instructions we provide. The syntax of this command is relatively simple and consists of three parts: options, a script containing the Linux command to be run, and a file name.

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