Basics

Running sed

sed 's/old/new/' file.txt          # substitute first match per line
sed 's/old/new/g' file.txt         # substitute all matches per line
sed -n '5p' file.txt               # print only line 5
sed '3d' file.txt                  # delete line 3
echo "hello" | sed 's/hello/hi/'   # pipe input

Command-Line Flags

-n	Suppress automatic printing; only print with `p`
-e 'cmd'	Execute a sed command (chain multiple with `-e`)
-f script.sed	Read commands from a file
-i[suffix]	Edit file in-place (optional backup suffix)
-E / -r	Use extended regular expressions

Substitution

Substitution Syntax

sed 's/foo/bar/' f                 # first occurrence per line
sed 's/foo/bar/g' f                # all occurrences
sed 's/foo/bar/3' f                # 3rd occurrence only
sed 's/foo/bar/gi' f               # all, case-insensitive
sed 's|/usr/bin|/opt/bin|g' f      # alternate delimiter

Substitution Flags

g	Replace all occurrences on the line
N (number)	Replace only the Nth occurrence
p	Print line if substitution was made
w file	Write substituted lines to file
i / I	Case-insensitive match (GNU)

Addresses

Address Examples

sed '3s/a/b/' f                    # only on line 3
sed '2,5s/a/b/' f                  # lines 2 through 5
sed '/^#/d' f                      # delete lines starting with #
sed '/start/,/end/d' f             # delete range between patterns
sed '1~2d' f                       # delete odd-numbered lines (GNU)

Address Types

N	Line number N
$	Last line
N,M	Line range from N to M
/regex/	Lines matching regex
/regex1/,/regex2/	Range from first match to second match
N~step	Starting at N, every step-th line (GNU)
addr!	Negate — apply to non-matching lines

Delete & Print

Delete & Print Commands

sed '5d' f                         # delete line 5
sed '/^$/d' f                      # delete blank lines
sed -n '10,20p' f                  # print lines 10–20
sed -n '/error/p' f                # print lines matching pattern
sed '/debug/!d' f                  # keep only matching lines

Command Reference

d	Delete pattern space, start next cycle
D	Delete up to first newline in pattern space
p	Print pattern space
P	Print up to first newline in pattern space
q	Quit after printing current pattern space
Q	Quit without printing (GNU)

Insert & Append

Insert, Append, Change

sed '3i\inserted line' f           # insert before line 3
sed '3a\appended line' f           # append after line 3
sed '3c\replaced line' f           # replace line 3
sed '/marker/a\new line' f         # append after pattern match

Commands

i\text	Insert text before current line
a\text	Append text after current line
c\text	Replace current line with text
r file	Read and append contents of file
R file	Read and append one line from file (GNU)
w file	Write pattern space to file

Hold Space

Hold Space Commands

h	Copy pattern space to hold space
H	Append pattern space to hold space
g	Copy hold space to pattern space
G	Append hold space to pattern space
x	Exchange pattern and hold spaces

Hold Space Examples

sed -n '1!G;h;$p' f               # reverse lines (tac)
sed '/^$/{ x; s/\n//; x; }' f     # collapse hold on blank
sed -n 'H;${x;s/\n/ /g;p;}' f     # join all lines with space

Multiple Commands

Chaining Commands

sed -e 's/foo/bar/g' -e 's/baz/qux/g' f
sed 's/foo/bar/g; s/baz/qux/g' f
sed '/header/{ s/old/new/; s/foo/bar/; }' f
sed -f commands.sed input.txt

Grouping & Branching

{ cmd1; cmd2; }	Group commands for same address
:label	Define a branch label
b label	Branch (jump) to label
t label	Branch if last `s///` succeeded
T label	Branch if last `s///` failed (GNU)

In-place Editing

In-place Examples

sed -i 's/old/new/g' file.txt            # edit in place (GNU)
sed -i.bak 's/old/new/g' file.txt        # backup as file.txt.bak
sed -i '' 's/old/new/g' file.txt         # macOS in-place (no backup)
sed -i '/^#/d' config.txt                # remove comments in place

Platform Notes

GNU sed -i	Suffix is optional; `-i` alone edits without backup
BSD/macOS sed -i	Requires suffix argument; use `-i ''` for no backup
-i.bak	Creates backup file with `.bak` extension
Multiple files	`sed -i 's/a/b/g' *.txt` edits all matching files

Regex

Regex in sed

.	Any single character
*	Zero or more of preceding
\+	One or more (BRE) — `+` in ERE
\?	Zero or one (BRE) — `?` in ERE
^	Start of line
$	End of line
[abc]	Character class
	Capture group (BRE) — `()` in ERE
\1, \2	Back-reference to capture group
&	Entire matched string (in replacement)

Regex Examples

sed 's/[0-9]\+/NUM/g' f               # replace numbers
sed -E 's/(foo)(bar)/\2\1/g' f         # swap groups (ERE)
sed 's/.*/(&)/' f                      # wrap line in parens
sed 's/[ \t]*$//' f                    # strip trailing whitespace

Common Patterns

One-Liners

sed -n '1p' f                          # first line (head -1)
sed '$!d' f                            # last line (tail -1)
sed '/^$/d' f                          # remove blank lines
sed 's/^[ \t]*//' f                    # strip leading whitespace
sed '=' f | sed 'N;s/\n/\t/' f         # number lines

Recipes

Double-space	`sed G` — append blank line after each line
Remove HTML tags	`sed 's/<[^>]*>//g'`
Extract emails	`sed -nE 's/.([a-z]+@[a-z.]+)./\1/p'`
Comment lines	`sed 's/^/# /'` — prefix each line with `#`
Trim blank lines at EOF	`sed -e :a -e '/^\n*$/{$d;N;ba' -e '}'`
Replace nth line	`sed 'Nc\new text'` — replace line N

SED QUICK REFERENCE