Text Manipulation:

GNU sed recipes

Summary

GNU sed (stream editor) is a powerful text processing tool commonly used for parsing, modifying, and transforming text streams in Unix-based systems. This article provides a collection of useful command examples and sed recipes with detailed explanations and examples.

Published:

2019-08-19

Updated:

2025-02-16

Reading time:

02:45

Author:

Jonas Jared Jacek

Tags:

linux, scripting

License:

CC BY-SA 4.0

Permalink:

GNU sed recipes

What is sed? #

GNU sed, or the stream editor, is a command-line text processing tool that operates on streams of text input. It reads text from a specified source, applies specified editing commands, and then outputs the modified text.

sed is a powerful and versatile tool for text manipulation in Unix-like environments. Check the GNU sed cheat sheet for even more sed command examples.

Basic usage #

The general syntax of sed is:

sed [options] 'command' file

Print specific lines #

To print only a specific line from a file:

sed -n '5p' file.txt

This prints the 5th line from file.txt.

To print a range of lines (e.g., lines 5 to 10):

sed -n '5,10p' file.txt

Substitutions #

Basic find and replace #

sed 's/old/new/' file.txt

This replaces the first occurrence of “old” with “new” on each line.

Global replacement #

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

This replaces all occurrences of “old” with “new” on each line.

Case-insensitive replacement #

sed 's/old/new/gi' file.txt

The i flag makes the substitution case-insensitive.

Replace in a specific line #

sed '5s/old/new/' file.txt

This replaces “old” with “new” only in the 5th line.

Deleting lines #

sed recipes for removing/deleting lines from a file following one or more expressions, invoked by the -e / --expression= operator.

sed does not remove the lines from the source file by default. Use the -i option with the sed command to work on the source file. Alternatively, use redirection to save the output to a new file, e.g. sed '1d' file > newfile.

Delete a specific line #

sed '5d' file.txt

Deletes the 5th line from the file.

Delete a range of lines #

sed '5,10d' file.txt

Deletes lines from 5 to 10.

Delete empty lines #

sed '/^$/d' file.txt

Removes all empty lines.

Delete lines that begin with a specified character #

sed '/^a/d' file.txt

Deletes lines that begin with “a”.

Delete lines that end with a specified character #

sed '/a$/d' file.txt

Deletes lines that end with “a”.

Delete lines where contents are written in upper case #

sed '/^[A-Z]*$/d' file.txt

Deletes lines that contain only uppercase letters.

Delete lines that contain a specific pattern #

sed '/foobar/d' file.txt

Deletes lines that contain the pattern “foobar”.

Delete lines starting from a pattern till the last line #

sed '/foobar/,$d' file.txt

Deletes lines starting from “foobar” to the last line.

Inserting and appending text #

Insert a line before a specific line #

sed '5i\New line inserted' file.txt

Inserts “New line inserted” before line 5.

Append a line after a specific line #

sed '5a\New line appended' file.txt

Appends “New line appended” after line 5.

Modifying lines #

Change a specific line #

sed '5c\This is the new content' file.txt

Replaces the entire 5th line with “This is the new content”.

Replace text in multiple files #

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

The -i option modifies files in place. This replaces “old” with “new” in all .txt files.

Advanced patterns #

Replace only if a pattern matches #

sed '/pattern/s/old/new/' file.txt

Replaces “old” with “new” only in lines that contain “pattern”.

Replace using regular expressions #

sed -E 's/[0-9]+/NUMBER/g' file.txt

This replaces all numeric sequences with “NUMBER”.

Extracting parts of a file #

Extract all email addresses:

sed -nE 's/.*([a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}).*/\1/p' file.txt

Working with delimiters #

If your pattern contains /, use an alternative delimiter:

sed 's|/usr/local/bin|/opt/bin|g' file.txt

Using | instead of / avoids confusion.

Further readings #

Sources and recommended, further resources on the topic:

• GNU: sed home page
• GNU: sed manual
• GNU sed cheat sheet

Author

Jonas Jared Jacek (J15k)

Jonas works as project manager, web designer, and web developer since 2001. On top of that, he is a Linux system administrator with a broad interest in things related to programming, architecture, and design. See: https://www.j15k.com/

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