The Linux sed command (Stream Editor) command is perhaps the most versatile and strong tool in the Unix-based operating systems. With it, you can search, replace, remove, and otherwise manipulate text quickly within files or standard input streams.
Regardless of whether you are a new Linux user or a seasoned one, mastering Linux sed command can really help advance your productivity when working with text manipulation and automation. This tutorial will guide you through all the things you should know about sed, from the fundamentals to the advanced methods.
What is sed?
sed is an abbreviation for Stream Editor. Unlike a traditional text editor, sed works on streams of text and supports on-the-fly modification without the need to open a file in an interactive editor. This makes it very efficient for batch processing and automation purposes.
Some of the most important features of Linux sed command are:
- Text searching and replacement
- Deletion of certain lines
- Insertion and appending
- Extraction of certain portions of a file
- Multiple editing rules applied simultaneously
Basic Syntax of sed
The overall syntax for the Linux sed command is:
sed [OPTIONS] 'COMMAND' file
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- OPTIONS: Adjust sed’s behavior (such as activating in-place editing).
- COMMAND: Specifies what sed is supposed to do (substitution, delete, etc.).
- file: The file to operate on (optional; sed can also accept input from stdin).
sed may also be used with pipelines:
echo "Hello World" | sed 's/World/Linux/'
This prints:
1. Replacing Text with sed
Basic Substitution (s command)
The most frequent usage of Linux sed command is replacing text using the s command:
sed 's/old_text/new_text/' file.txt
This substitutes the first instance of old_text with new_text in every line of file.txt.
Example:
echo "I love Java" | sed 's/Java/Linux/'
Output:
Global Replacement (g flag)
By default, Linux sed command only substitutes the first match of a pattern in a line. To substitute all matches, use the g flag:
sed 's/foo/bar/g' file.txt
Example:
echo "foo foo foo" | sed 's/foo/bar/g'
Output:
Case-Insensitive Replacement (I flag)
To replace case-insensitively, use the I flag:
echo "Hello HELLO hello" | sed 's/hello/world/Ig'
Output:
2. Deleting Lines with sed
Delete a Specific Line
To delete a particular line (e.g., line 3):
sed '3d' file.txt
Delete Lines Matching a Pattern
To delete lines with a given word:
sed '/error/d' file.txt
Delete a Range of Lines
To delete several lines (e.g., lines 2 to 5):
sed '2,5d' file.txt
Delete Blank Lines
To delete all blank lines:
sed '/^$/d' file.txt
Inserting and Appending Text
Insert a Line Before a Specific Line (i command)
sed '3i This is a new line' file.txt
This inserts “This is a new line” before line 3.
Append a Line After a Specific Line (a command)
sed '3a This is an appended line' file.txt
This inserts “This is an appended line” after line 3.
4. Extracting and Displaying Text
Print Specific Lines
To print only line 5:
sed -n '5p' file.txt
To print lines 3 to 7:
sed -n '3,7p' file.txt
To print lines with “error”:
sed -n '/error/p' file.txt
Print Every 3rd Line
sed -n '0~3p' file.txt
5. Handling Multiple Commands
You can use multiple sed commands with ; or -e:
sed -e 's/foo/bar/g' -e '3d' file.txt
Or use {} for readability:
sed -e '
s/foo/bar/g
3d
' file.txt
6. In-Place Editing (-i flag)
By default, sed does not modify files in place. To edit files in-place:
sed -i 's/error/warning/g' file.txt
To save a copy of the original file:
sed -i.bak 's/error/warning/g' file.txt
7. Advanced sed Tricks
Replace Only on Specific Line
To replace “foo” with “bar” only on line 3:
sed '3s/foo/bar/' file.txt
Replace Only the Last Occurrence
sed ':a; $!N; s/foo/bar/; ta' file.txt
Swap Two Words
sed 's/(word1)\ (word2)/\2 \1/' file.txt
8. Combining sed with Other Commands
Replace Text in Multiple Files
sed -i 's/old/new/g' .txt Using find and sed Together bash Copy Edit find. -name ".txt" -exec sed -i 's/foo/bar/g' {} +
Extract Email Addresses from a File
sed -nE 's/.([a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,6})./\1/p' file.txt
Conclusion
The linux sed command is a very powerful text processing tool in Linux. Whether you’re doing simple find-and-replace or complicated text manipulation, sed can do it efficiently. Mastering sed will enable you to automate tedious tasks, scrub data, and manipulate text files like a pro.
FAQs
1. What is sed in Linux?
Linux sed (Stream Editor) is a command with great power used to process and edit text from files or stdin. It facilitates searching, substituting, inserting, deleting, and manipulating text in an effective manner.
2. How do I use sed?
sed processes line by line, performs specified commands (such as substitution or deletion), and prints the transformed text. It does not alter files by default unless -i is used.
3. How do I delete special characters from a file?
To delete all non-alphanumeric characters:sed 's/[^a-zA-Z0-9 ]//g' file.txt
