Linux `sed` Command Tutorial – Text Manipulation Made Easy

The `sed` (Stream Editor) command is a powerful tool in Linux for editing and manipulating text files. It allows you to perform tasks like searching, replacing, inserting, and deleting text within files using a simple command-line interface.

1. What is `sed`?

`sed` stands for Stream Editor. It reads input from a file or standard input, processes it line by line, and outputs the results. It's commonly used for text transformation and automation in shell scripts.

2. Basic `sed` Syntax

The basic syntax of `sed` is:

sed [options] 'command' filename

- options are flags like `-i` (in-place editing), `-n` (suppress automatic output), etc. - command is the action you want to perform (e.g., replace, insert, delete). - filename is the name of the file you want to edit.

3. Common `sed` Commands

3.1. Replace Text in a File

To replace all occurrences of a word in a file:

sed 's/old/new/g' filename.txt

- s stands for substitute. - old is the text you want to replace. - new is the text you want to replace it with. - g stands for global (replace all occurrences in the line).

3.2. Replace in Multiple Files

To replace text in multiple files:

sed -i 's/old/new/g' file1.txt file2.txt

The -i option edits the file in-place.

3.3. Delete Lines

To delete lines matching a pattern:

sed '/pattern/d' filename.txt

- /pattern/d deletes all lines that match the pattern.

3.4. Insert Text

To insert text at the beginning of a file:

sed '1i\This is a new line' filename.txt

- 1i inserts text before line 1. - You can also use i to insert at the top of the file.

3.5. Append Text

To append text at the end of a file:

<
ode>sed '$a\This is a new line at the end' filename.txt

- $a appends text after the last line.

3.6. Search and Replace with Regular Expressions

`sed` supports regular expressions for more complex replacements:

sed 's/[0-9]/X/g' filename.txt

This replaces all digits with the letter "X".

3.7. Substitute Multiple Patterns

You can replace multiple patterns in a single command:

sed -e 's/old1/new1/g' -e 's/old2/new2/g' filename.txt

4. Practical Use Cases

4.1. Replace a Word in a File

Replace all instances of "hello" with "hi" in example.txt:

sed 's/hello/hi/g' example.txt

4.2. Replace in Multiple Files

Replace "old" with "new" in all .txt files:

sed -i 's/old/new/g' *.txt

4.3. Delete Lines Containing a Specific Word

Delete all lines with the word "error" in log.txt:

sed '/error/d' log.txt

4.4. Insert a Line at the Top of a File

Insert a line at the top of file.txt:

sed '1i\This is the new line' file.txt

5. Advanced Features

5.1. Use `sed` with `grep` for Filtering

Combine `sed` with `grep` to filter and modify text:

grep 'pattern' filename.txt | sed 's/pattern/replacement/g'

5.2. Use `sed` in Shell Scripts

`sed` is often used in shell scripts for automation:

#!/bin/bash
sed -i 's/old/new/g' file.txt
echo "Text replaced in file.txt"

6. Summary

The `sed` command is a powerful tool for text manipulation in Linux. Whether you're replacing text, deleting lines, or inserting content, `sed` provides a flexible and efficient way to handle these tasks from the command line. With practice, you'll find it to be one of the most useful commands in your Linux toolkit.