What does sed command do?

The sed command, which stands for "stream editor," is a powerful text-processing utility in Unix-like operating systems. It is used to perform various text transformations on an input stream (a file or data received through a pipeline) and produce an output stream. sed operates on a line-by-line basis, allowing you to apply changes to specific lines that match patterns or conditions. Some common tasks that sed can perform include:

Search and Replace: sed can search for a specific pattern (regular expression) in the input and replace it with another string. For example:

sed 's/search_string/replace_string/g' input.txt

Delete Lines: sed can delete lines from the input that match a particular pattern or condition. For example:

sed '/pattern_to_delete/d' input.txt

Insert Lines: sed can insert new lines before or after specific lines or patterns in the input. For example:

sed '/pattern_to_insert_before/i new_line_text' input.txt

Append Lines: sed can append new lines after specific lines or patterns in the input. For example:

sed '/pattern_to_insert_after/a new_line_text' input.txt

Selecting Lines: sed can select and print only specific lines from the input that match certain criteria. For example:

sed -n '/pattern_to_select/p' input.txt

Substitution with Regular Expressions: sed can perform complex substitutions using regular expressions. It supports patterns, groups, and various substitution options.

In-Place Editing: With the -i option, sed can edit files in-place, making changes directly to the file without the need for temporary files.

Multiple Operations: You can chain multiple sed commands together using semicolons to perform a series of text transformations in one go.

Here's a basic example of using sed to replace text in a file:

sed 's/old_text/new_text/g' input.txt > output.txt

In this command, sed searches for occurrences of "old_text" in the "input.txt" file and replaces them with "new_text." The modified text is then redirected to "output.txt."

sed is a versatile tool for text manipulation and can be used for various text-processing tasks in shell scripting and system administration. It's known for its flexibility and can handle complex text transformations using regular expressions and patterns.

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