How to Use the sed Command in Linux

Stands for “Stream Editor”. “sed” is a utility command that take file content or standard input (stdin) and modify the output through RegEx pattern. It’s generally a handy command to use to modify content within a file.

General syntax for sed command:

$ sed [OPTIONS] [FILE]...

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: Finding the word “CSS” in the text “CSS Libraries” and replacing it with the word “JavaScript.”

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 replace the word “harder” in the first line of the libraries.txt file. Note: “harder” occurs twice in the line.

Replace first matching with new text

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

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

Example: Replacing the first occurrence of the word “CSS” in the example.txt file with the word “JavaScript”

Remove matching lines

sed '/Something/d' example.txt

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

Example: Deleting those lines in the example.txt file that contain the text “Something”

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: Finding a line containing the word ‘Sample’ and seeing the line delete with and without option in the example.txt file.

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: Searching for the word “libraries” in the example.txt file and replacing it with uppercase letters.

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: Searching for the word “libraries” in the example.txt file and replacing it with lowercase letters.

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: Displaying the file before using the option. Then we use the command and see that after each line, empty lines appeared.

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: Following the use of the command, the line numbers appear after each line in the example.txt file.