Linux sed Command

The sed command in Linux stands for “Stream Editor”. It is used to perform basic text transformations on an input stream (a file or input from a pipeline). sed is extremely powerful for tasks like finding and replacing text, inserting or deleting lines, and more — all done automatically without opening files manually.

It processes text line by line, allowing you to perform automatic edits on files or input streams without manually opening them. It’s especially useful for repetitive text transformations, substitutions, or deletions.

sed Command

• sed is designed for parsing and transforming text.
• It reads text line-by-line and applies operations specified in its command.
• It is widely used for text processing tasks like search, replace, delete, and insert.
• sed can be used directly from the terminal or in shell scripts.
• Changes made by sed are by default temporary unless redirected to a new file.
• Works with regular expressions for pattern matching.
• Does not modify the original file by default (outputs to stdout).

Command Syntax

The general synatx is as follows:

$ sed [options] 'command' filename

Explanation:

• options – Optional flags to modify sed behavior (like -i for in-place editing).
• command – The sed instruction to perform (like substitute, delete, insert).
• filename – The name of the file on which the sed command will operate.

Examples

Replacing Text

$ sed 's/oldtext/newtext/' filename

Example:

$ sed 's/apple/banana/' fruits.txt

This will replace the first occurrence of “apple” with “banana” in each line of the file fruits.txt.

 

Replacing All Occurrences in a Line

$ sed 's/oldtext/newtext/g' filename

Example:

$ sed 's/apple/orange/g' fruits.txt

Here, g stands for global, meaning all instances of “apple” in a line will be replaced.

Deleting Lines Containing a Specific Word

$ sed '/word/d' filename

Example:

$ sed '/banana/d' fruits.txt

This will delete all lines containing the word “banana”.

Printing Only Specific Lines

$ sed -n '2,4p' filename

Example:

$ sed -n '2,4p' fruits.txt

This will print only lines 2 to 4 from the file.

sed vs awk

Some of the differences between sed and awk are as follows:

	sed	awk
Purpose	Stream editor for simple text transformations	Pattern scanning and processing language
Focus	Line-by-line editing	Field-by-field data processing
Complexity	Simple substitutions and deletions	Advanced text processing, calculations, and reports
Syntax	Compact and simple	More programming-like with variables and control structures
Use Case Example	Replace words, delete lines	Summarize column data, conditional formatting