How to Use the sed Command in Linux

The name sed stands for “Stream Editor,” and it’s a powerful utility that allows you to parse and transform text right from the command line. Whether you’re dealing with configuration files, scripts, or even plain text, sed is your go-to tool for quick and efficient text manipulation.

The primary use of sed is to search for specific patterns of text and replace them with something else. It can also delete or insert lines and perform other text transformations. It’s particularly useful for batch editing of files or for working within shell scripts to automate various tasks.

While sed is incredibly versatile on its own, it’s often used in combination with other Linux commands like awk for text processing, grep for pattern searching, and cat for displaying file content. Together, these tools form a robust toolkit for text processing in the Linux environment.

General syntax for sed command:

$ sed [OPTIONS] [FILE]...

1. Text substitution

echo "Text" | sed 's/Replaceable_Word/The_Word_That_Replaces/'

Use the sed command to search and replace any part of the text. 's' indicates a search and replace task.

Example:

Let’s say you have a string “I love CSS” and you want to replace “CSS” with “CSS Libraries“.

echo "I love CSS" | sed 's/CSS/CSS Libraries/'

I love CSS Libraries

In this example, the echo command outputs “I love CSS“, and then sed replaces “CSS” with “CSS Libraries“. The final output is “I love CSS Libraries“.

2. Replace text on a specific line in a file

sed '[line] s/harder/easier/g' [file]

The 'g' option of the sed command is used to replace anything that matches the pattern.

Example:

Let’s say you have a text file named example.txt with the following content:

Life is hard.
Working harder is the key to success.
The harder you work, the luckier you get.

To replace all occurrences of the word “harder” with “easier” on line 2 of example.txt, you would run:

sed '2 s/harder/easier/g' example.txt

After running the command, the output displayed on the terminal would be:

Life is hard.
Working easier is the key to success.
The harder you work, the luckier you get.

Note that the word “harder” is replaced with “easier” only on line 2.

If you want to save these changes back to the file, you can use the -i option:

sed -i '2 s/harder/easier/g' example.txt

After running this command, the content of example.txt will be permanently changed to:

Life is hard.
Working easier is the key to success.
The harder you work, the luckier you get.

3. Replace first matching with new text

sed 's/harder/easier/' [file]

This command replaces only the first match of the search pattern.

Example:

Let’s say you have a text file named example.txt with the following content:

Life is harder than we think.
Working harder is the key to success.
No pain, no gain. Work harder.

You can use the sed command to replace the word “harder” with “easier” in each line:

sed 's/harder/easier/' example.txt

After running the command, the output will be:

Life is easier than we think.
Working easier is the key to success.
No pain, no gain. Work easier.

4. Remove matching lines

sed '/Something/d' example.txt

Use the d option of the sed command to remove any line from a file.

Example:

Let’s say you have a file called example.txt with the following content:

Hello World
Something is here
Another line
Yet another line
Something else

Running the command sed '/Something/d' example.txt will output:

Hello World
Another line
Yet another line

5. Search for a case-insensitive word + delete it

sed '/Sample/Id' example.txt

The I option of the sed command is used to search for a matching pattern in a case insensitive way.

Example:

Let’s say you have a file named example.txt with the following content:

This is a Sample line.
Another line.
Yet another Sample line.
Final line.

Running the command sed '/Sample/Id' example.txt will produce the following output:

Another line.
Final line.

6. Replace words with uppercase

sed 's/\(libraries\)/\U\1/Ig' example.txt

Use the U option of the sed command to convert any text to uppercase letters.

Example:

Let’s say you have a file named example.txt with the following content:

I love libraries.
libraries are great.
You can find many books in libraries.

After running the sed command, the output will be:

I love LIBRARIES.
LIBRARIES are great.
You can find many books in LIBRARIES.

7. Replace words with lowercase

sed 's/\(libraries\)/\L\1/Ig' example.txt

The L option of the sed command is used to convert any text to lowercase letters.

Example:

Let’s say you have a file named example.txt with the following content:

Libraries are essential for research.
libraries help in many ways.
I love LIBRARIES!

After running the sed command, the output will be:

libraries are essential for research.
libraries help in many ways.
I love libraries!

8. Insert blank lines in a file

sed G [file]

Use the G option of the sed command to insert blank lines after each line of the file.

Example:

Let’s say you have a file called example.txt with the following content:

Hello
World
This
Is
A
Test

You can run the following command to append an extra newline at the end of each line:

sed G example.txt

After running the command, the output will be:

Hello

World

This

Is

A

Test

9. Print file’s line numbers

sed '=' [file]

The = sign is used to print a line number before each line of text in a file.

Example:

Let’s say you have a file named example.txt with the following content:

Hello
World
This
Is
A
Test

You can run the following command to print the line numbers before each line:

sed '=' example.txt

1
Hello
2
World
3
This
4
Is
5
A
6
Test

More Linux commands: