| The stream editor, sed, is a noninteractive editor. It interprets a script and performs the actions in the script. sed is stream-oriented because, like many Unix programs, input flows through the program and is directed to standard output. For example, sort is stream-oriented; vi is not. sed's input typically comes from a file or pipe but it can also be taken from the keyboard. Output goes to the screen by default but can be captured in a file or sent through a pipe instead. GNU sed can edit files that use multibyte character sets. 10.1.1. Typical Uses of sed Editing one or more files automatically. Simplifying repetitive edits to multiple files. Writing conversion programs.
10.1.2. sed Operation sed operates as follows: Each line of input is copied into a "pattern space," an internal buffer where editing operations are performed. All editing commands in a sed script are applied, in order, to each line of input. Editing commands are applied to all lines (globally) unless line addressing restricts the lines affected. If a command changes the input, subsequent commands and address tests are applied to the current line in the pattern space, not the original input line. The original input file is unchanged because the editing commands modify an in-memory copy of each original input line. The copy is sent to standard output (but can be redirected to a file). sed also maintains the "hold space," a separate buffer that can be used to save data for later retrieval.
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