sed Command Cheat Sheet

sed (Stream Editor) is a powerful text stream editor for filtering and transforming text. It performs basic text manipulation on files and streams without opening the file in an editor. Perfect for automated editing and text processing in scripts.

Synopsis

sed [OPTIONS] 'command' [file...]
sed [OPTIONS] -e 'command1' -e 'command2' [file...]
sed [OPTIONS] -f scriptfile [file...]

Description

sed reads input line by line, applies editing commands to each line, and writes the result to standard output. It's commonly used for search-and-replace operations, selective printing, and in-place file modifications.

Basic Substitution

Replace First Occurrence

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

Output shows replacement on first match per line.

Replace All Occurrences (Global)

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

The g flag makes substitution global on each line.

Replace Nth Occurrence

# Replace second occurrence on each line
sed 's/old/new/2' file.txt

# Replace from second occurrence onward
sed 's/old/new/2g' file.txt

Case-Insensitive Replace

sed 's/old/new/gi' file.txt
sed 's/old/new/I' file.txt  # Alternative

In-Place Editing

Modify File Directly

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

Create Backup Before Editing

# Linux/GNU sed
sed -i.bak 's/old/new/g' file.txt

# macOS/BSD sed
sed -i '.bak' 's/old/new/g' file.txt

Creates file.txt.bak with original content.

Line Addressing

Specific Line Number

# Substitute only on line 3
sed '3s/old/new/' file.txt

# Delete line 5
sed '5d' file.txt

Line Range

# Lines 1 to 5
sed '1,5s/old/new/g' file.txt

# From line 10 to end
sed '10,$s/old/new/g' file.txt

Pattern Matching

# Lines containing "pattern"
sed '/pattern/s/old/new/g' file.txt

# Lines NOT containing "pattern"
sed '/pattern/!s/old/new/g' file.txt

Line Range Between Patterns

# From first occurrence of start to first occurrence of end
sed '/start/,/end/s/old/new/g' file.txt

Deletion Commands

Delete Specific Lines

# Delete line 3
sed '3d' file.txt

# Delete lines 2-5
sed '2,5d' file.txt

# Delete last line
sed '$d' file.txt

Delete Lines Matching Pattern

# Delete lines containing "pattern"
sed '/pattern/d' file.txt

# Delete empty lines
sed '/^$/d' file.txt

# Delete lines starting with #
sed '/^#/d' file.txt

# Delete lines containing only whitespace
sed '/^[[:space:]]*$/d' file.txt

Print Commands

Print Specific Lines

# Print line 5 only
sed -n '5p' file.txt

# Print lines 10-20
sed -n '10,20p' file.txt

# Print last line
sed -n '$p' file.txt

Print Lines Matching Pattern

# Print lines containing "error"
sed -n '/error/p' file.txt

# Like grep, but with sed
sed -n '/ERROR/p' log file.txt

Print with Line Numbers

sed -n '=' file.txt  # Line numbers only
sed = file.txt | sed 'N;s/\n/ /'  # Numbers with content

Insert and Append

Insert Line Before

# Insert before line 3
sed '3i\New line text' file.txt

# Insert before lines matching pattern
sed '/pattern/i\New line' file.txt

Append Line After

# Append after line 3
sed '3a\New line text' file.txt

# Append after matching pattern
sed '/pattern/a\New line' file.txt

Multiple Lines

# Insert multiple lines
sed '3i\Line 1\nLine 2\nLine 3' file.txt

# Append multiple lines
sed '5a\First line\nSecond line' file.txt

Change (Replace) Lines

Replace Entire Line

# Replace line 3
sed '3c\Completely new line' file.txt

# Replace lines matching pattern
sed '/pattern/c\Replacement line' file.txt

# Replace line range
sed '5,10c\One line replaces all' file.txt

Multiple Commands

Using -e Flag

sed -e 's/foo/bar/' -e 's/hello/goodbye/' file.txt

Using Semicolon

sed 's/foo/bar/; s/hello/goodbye/' file.txt

Using -f Script File

Create script.sed:

s/old1/new1/g
s/old2/new2/g
/pattern/d

Run:

sed -f script.sed file.txt

Advanced Substitution

Using Different Delimiters

# Useful for paths
sed 's|/old/path|/new/path|g' file.txt
sed 's#http://old#https://new#g' file.txt

Capture Groups and Backreferences

# Swap two words
sed 's/\([a-z]*\) \([a-z]*\)/\2 \1/' file.txt

# Extract part of pattern
echo "Email: user@example.com" | sed 's/.*:\s*\(.*\)/\1/'
# Output: user@example.com

Using & for Matched String

# Add quotes around matched word
sed 's/[a-zA-Z]*/\"&\"/' file.txt

# Add brackets around numbers
echo "Error 404" | sed 's/[0-9]*/[&]/'
# Output: Error [404]

Regular Expressions

Anchors

# Lines starting with "Error"
sed -n '/^Error/p' file.txt

# Lines ending with "done"
sed -n '/done$/p' file.txt

Character Classes

# Replace any digit
sed 's/[0-9]/X/g' file.txt

# Replace whitespace
sed 's/[[:space:]]/_/g' file.txt

# Remove non-alphanumeric
sed 's/[^a-zA-Z0-9]//g' file.txt

Quantifiers

# One or more digits
sed 's/[0-9]\+/NUM/g' file.txt

# Zero or more spaces
sed 's/[[:space:]]*$//' file.txt  # Trim trailing spaces

# Exactly 3 letters
sed 's/[a-z]\{3\}/XXX/g' file.txt

Practical Examples

Remove Comments

# Remove lines starting with #
sed '/^#/d' config.conf

# Remove inline comments
sed 's/#.*//' file.txt

# Remove both
sed -e '/^#/d' -e 's/#.*//' config.conf

Remove Blank Lines

# Remove empty lines
sed '/^$/d' file.txt

# Remove lines with only whitespace
sed '/^[[:space:]]*$/d' file.txt

# Squeeze multiple blank lines to one
sed '/^$/N;/^\n$/D' file.txt

Add Line Numbers

sed = file.txt | sed 'N;s/\n/\t/'

Convert DOS to Unix Line Endings

sed 's/\r$//' dosfile.txt > unixfile.txt
sed -i 's/\r$//' file.txt  # In-place

Convert Unix to DOS Line Endings

sed 's/$/\r/' unixfile.txt > dosfile.txt

Extract Email Addresses

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

Extract IP Addresses

sed -n 's/.*\([0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\).*/\1/p' log.txt

Replace Tabs with Spaces

sed 's/\t/    /g' file.txt  # 4 spaces

Join Lines

# Join lines ending with backslash
sed ':a;N;$!ba;s/\\\n//g' file.txt

# Join all lines
sed ':a;N;$!ba;s/\n/ /g' file.txt

Double Space File

sed 'G' file.txt

Remove Trailing Whitespace

sed 's/[[:space:]]*$//' file.txt

Number Non-Blank Lines

sed '/./=' file.txt | sed '/./N; s/\n/ /'

Working with Files

Edit Multiple Files

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

Process from Stdin

echo "Hello World" | sed 's/World/Universe/'

cat file.txt | sed 's/foo/bar/'

Output to Different File

sed 's/old/new/g' input.txt > output.txt

Advanced Features

Hold Space and Pattern Space

# Reverse file (like tac)
sed '1!G;h;$!d' file.txt

# Print every other line
sed 'n;d' file.txt  # Odd lines
sed '1d;n;d' file.txt  # Even lines

Labels and Branching

# Remove duplicate consecutive lines
sed '$!N; /^\(.*\)\n\1$/!P; D'

Conditional Execution

# Replace only if line contains "pattern"
sed '/pattern/{s/old/new/g;}' file.txt

Common Use Cases

Configuration Files

# Update configuration value
sed -i 's/^DEBUG=.*/DEBUG=True/' config.ini

# Add setting if not exists
sed -i '/^API_KEY=/!s/$/\nAPI_KEY=abc123/' .env

Log Processing

# Extract errors from log
sed -n '/ERROR/p' application.log

# Show last 100 lines with timestamp
tail -n 100 app.log | sed 's/^/['"$(date)"'] /'

HTML/XML Processing

# Remove HTML tags
sed 's/<[^>]*>//g' page.html

# Extract title
sed -n 's/.*<title>\(.*\)<\/title>.*/\1/p' page.html

CSV Processing

# Change delimiter from comma to pipe
sed 's/,/|/g' data.csv

# Remove quotes
sed 's/"//g' data.csv

# Extract specific column (2nd)
sed 's/[^,]*,\([^,]*\),.*/\1/' data.csv

Source Code

# Add copyright header
sed '1i\// Copyright 2024\n// All rights reserved\n' source.c

# Remove debug print statements
sed -i '/console\.log/d' script.js

# Comment out code lines
sed 's/^\(.*\)/# \1/' script.py

Tips and Best Practices

Test without -i first - View output before modifying files
Use backups - Always use -i.bak when editing important files
Quote commands - Single quotes prevent shell interpretation
Use different delimiters - Helpful when working with paths (s|/path|/new|)
Combine with other tools - Pipe with grep, awk, cut for powerful text processing
Extended regex - Use -E or -r for extended regular expressions
Script files - Use -f for complex multi-command operations

Options Summary

Option	Description
`-n`	Suppress automatic printing (use with `p`)
`-e`	Add script command
`-f`	Read script from file
`-i[SUFFIX]`	Edit files in-place (with optional backup)
`-r`, `-E`	Use extended regular expressions
`-s`	Treat files as separate (don't concatenate)
`-u`	Unbuffered output
`--posix`	Disable GNU extensions

Exit Status

Code	Meaning
0	Success
1	Invalid command, syntax error, or invalid regex
2	Input file could not be opened
4	I/O error