If you work with Linux, sooner or later you'll meet the mighty sed. It's a stream editor — meaning it processes text line by line — and it's incredibly useful for everything from simple search and replace to complex text manipulation.
Let’s dive deep, but crisp, into sed’s most powerful features. 🚀
🚀 What is sed?
sed stands for Stream EDitor. It reads input line-by-line, applies editing rules, and outputs the result. It doesn’t change the original file unless told to.
🔥 Basic Syntax:
sed [OPTIONS] 'command' file
🔍 Common sed Options
| Option | Description |
|---|---|
-n |
Suppress automatic printing (useful with p) |
-e |
Add multiple commands |
-i |
Edit file in-place (use with caution) |
-r or -E
|
Enable extended regex (more powerful patterns) |
🛠️ Most Used sed Commands
1. 🔄 Substitute (s)
sed 's/old/new/' file
- Replaces first occurrence of
oldwithnewon each line.
Flags:
-
g= replace all occurrences in a line -
i= case-insensitive -
p= print matched lines (use with-n)
sed 's/foo/bar/g' file # Replace all foo with bar
sed -n 's/foo/bar/p' file # Only print lines where replacement happened
2. 🧹 Delete Lines
sed '2d' file # Delete 2nd line
sed '1,3d' file # Delete lines 1 to 3
sed '/^$/d' file # Delete empty lines
sed '/pattern/d' file # Delete lines matching pattern
3. 🖨️ Print Lines
sed -n '2p' file # Print only line 2
sed -n '3,5p' file # Print lines 3 to 5
sed -n '/error/p' file # Print lines matching "error"
4. 🧵 Insert, Append, Change
sed '2i\New line' file # Insert before line 2
sed '2a\New line' file # Append after line 2
sed '2c\Changed line' file # Replace line 2 entirely
5. 🔃 Multiple Commands
sed -e 's/foo/bar/' -e 's/baz/qux/' file
# OR using curly braces
sed '1,3{ s/foo/bar/; s/baz/qux/ }' file
🎯 Address Ranges
You can target lines using:
- Specific numbers:
1,5 - Patterns:
/start/,/end/
sed '/BEGIN/,/END/d' file # Delete everything from BEGIN to END
🧠 Cool sed Tricks
✅ 1. Replace only Nth occurrence on each line
sed 's/foo/bar/2' file # Replace 2nd occurrence only
✅ 2. Replace text in-place
sed -i 's/foo/bar/g' file # Make permanent change to file
✅ 3. Remove leading/trailing whitespace
sed 's/^[ \t]*//;s/[ \t]*$//' file
✅ 4. Comment out all lines matching a pattern
sed '/pattern/s/^/#/' file
✅ 5. Add line numbers
nl file | sed 's/^[ \t]*//' # or:
sed = file | sed 'N;s/\n/ /'
📁 Real-Life Examples
💡 Replace a word in a config file
sed -i 's/localhost/127.0.0.1/g' config.cfg
💡 Delete all blank lines
sed '/^$/d' notes.txt
💡 Change HTML tags
sed 's/<b>/<strong>/g; s#</b>#</strong>#g' file.html
🧪 Testing sed Quickly
Use <<< to pass text directly:
sed 's/dog/cat/' <<< "I love my dog"
🧯 Safety Tip
When using -i, backup first!
sed -i.bak 's/error/ERROR/g' logfile.log
🏁 Final Words
sed is a scripting powerhouse. Start small — learn to replace, delete, and print — then go wild with multi-line editing, regex, and batch replacements.
Whether you're cleaning logs, transforming data, or tweaking config files, sed is your Linux Swiss Army knife. 🔪
💬 Got More sed Magic?
Drop your favorite sed one-liner in the comments!
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