Linux sed Command: Stream Editor

What is sed?

sed stands for Stream Editor. It is a powerful command-line tool used to process and modify text directly from the terminal without opening the file in an editor (like vi or nano).

With sed, you can find and replace text, delete lines, and insert new content : all without ever opening the file.

Basic Syntax

sed [options] 'command' filename

Find & Replace Operations

1. Replace Text (Without Modifying the Original File)

sed 's/Telusko/TeluskoAI/' telusko.txt

• Replaces Telusko with TeluskoAI and displays the output on the terminal.
• The original file is NOT changed : this is a preview of the changes.
• The replacement is case-sensitive.
• Replaces only the first occurrence of the pattern on each line.

2. Replace Text in the Original File (-i)

sed -i 's/Telusko/TELUSKOAI/' telusko.txt

• The -i flag makes the changes directly in the original file (in-place editing).
• The original file is modified permanently.
• Replaces only the first occurrence of the pattern on each line.

3. Replace All Occurrences on Each Line (g flag)

sed -i 's/telusko/learn.telusko.com/g' telusko.txt

• The g (global) flag replaces all occurrences of the pattern on every line, not just the first one.
• Combined with -i, the changes are applied directly to the file.

Delete Operations

1. Delete the Last Line ($d)

sed -i '$d' telusko.txt

• $ refers to the last line of the file.
• d is the delete command.
• This removes the last line from the file.

2. Delete a Specific Line (nd)

sed -i '2d' telusko.txt

• Deletes the 2nd line from the file.
• Replace 2 with any line number n to delete that specific line.

Insert Operations

1. Insert Text at a Specific Line (i\)

sed -i '4i\telusko has recorded and live courses' telusko.txt

• Inserts the given text at line 4 of the file.
• Existing content from line 4 onward is shifted down.

2. Append Text at the End of the File ($a\)

sed -i '$a\Muskan is also a part of the course' telusko.txt

• $a\ appends the given text after the last line of the file.

Quick Reference

Summary

• sed allows you to edit files directly from the terminal without opening them.
• Without -i, sed only displays the modified output : the original file remains unchanged.
• With -i, the changes are applied directly to the original file.
• Use the g flag to replace all occurrences on each line (not just the first).
• sed can replace, delete, and insert content : making it a versatile tool for text processing and automation.

Written By: Muskan Garg