Sed is a stream editor. A stream editor is used to perform basic text transformations on an input stream – a file or input from a pipeline. Sed operates by performing the instructions specified in a script on the input stream, line by line.
Sed is typically used for extracting part of a file using patterns, substituting multiple occurrences of a string within a file, deleting selected lines of a file, and inserting/appending text to the start or end of a line. In addition, Sed can be used to perform more complex transformations, such as converting a file from one format to another.
Sed is a powerful tool for manipulating text and is very useful for processing log files, configuration files, and other text files where simple transformations are required. However, Sed is not a programming language, so it is not suitable for more complex tasks.
If you need to perform complex text processing, you should use a proper programming language such as Perl, Python, or Ruby.