sed

sed is a stream editor for Unix-like operating systems

Getting started

sed is a stream editor for Linux and Unix-like operating systems.

Sed Usage

Syntax

$ sed [options] command [input-file]

With pipeline

$ cat report.txt | sed 's/Nick/John/g'

$ echo '123abc' | sed 's/[0-9]+//g'

Option Examples

Option	Example	Description
`-i`	sed -ibak ‘s/On/Off/’ php.ini	Backup and modify input file directly
`-E`	sed -E ‘s/[0-9]+//g’ input-file	Use extended regular expressions
`-n`	sed -n ‘3 p’ config.conf	Suppress default pattern space printing
`-f`	sed -f script.sed config.conf	Execute sed script file
`-e`	sed -e ‘command1’ -e ‘command2’ input-file	Execute multiple sed commands

Multiple commands

$ echo "hello world" | sed -e 's/h/H/g' -e 's/w/W/g'
Hello World

Use -e to execute multiple sed commands

Sed script

$ echo 's/h/H/g' >> hello.sed
$ echo 's/w/W/g' >> hello.sed 
$ echo "hello world" | sed -f hello.sed Hello World

Use -f to execute sed script file

Examples

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

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

See: Sed examples

Sed commands

Commands

Command	Example	Description
`p`	sed -n ‘1,4 p’ input.txt	Print lines 1-4
`p`	sed -n -e ‘1,4 p’ -e ‘6,7 p’ input.txt	Print lines 1-4 and 6-7
`d`	sed ‘1,4 d’ input.txt	Print lines except 1-4
`w`	sed -n ‘1,4 w output.txt’ input.txt	Write pattern space to file
`a`	sed ‘2 a new-line’ input.txt	Append line after
`i`	sed ‘2 i new-line’ input.txt	Insert line before

Space commands

Command	Description
`n`	Print pattern space, empty pattern space, and read next line
`x`	Swap pattern space with hold space
`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

Flags

$ sed 's/old/new/[flags]' [input-file]

Flag	Description
`g`	Global substitution
`1,2...`	Substitute the nth occurrence
`p`	Print only the substituted line
`w`	Write only the substituted line to a file
`I`	Ignore case while searching
`e`	Substitute and execute in the command line

Loops commands

Command	Description
`b label`	Branch to a label (for looping)
`t label`	Branch to a label only on successful substitution (for looping)
`:label`	Label for the b and t commands (for looping)
`N`	Append next line to pattern space
`P`	Print 1st line in multi-line
`D`	Delete 1st line in multi-line

Misc Flags

Flag	Description
`/ \| ^ @ ! #`	Substitution delimiter can be any character
`&`	Gets the matched pattern
`( ) \1 \2 \3`	Group using `(` and `)`. Use `\1`, `\2` in replacement to refer the group

Sed examples

Replacing text

Replace all occurrences of a string

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

Replace only the nth occurrence of a string

$ sed 's/old/new/2' file.txt

Replace replace a string only on the 5th line

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

Replace “world” with “universe” but only if the line begins with “hello”

$ sed '/hello/s/world/universe/' file.txt

Remove “" from the end of each line

$ sed 's/\\$//' file.txt

Remove all whitespace from beginning of each line

$ sed 's/^\s\*//' file.txt

Remove comments. Even those that are at the end of a line

$ sed 's/#.*$//' file.txt

Search for text

Search for a string and only print the lines that were matched

$ sed -n '/hello/p' file.txt

Case insensitive search

$ sed -n '/hello/Ip' file.txt

Search for a string but only output lines that do not match

$ sed -n '/hello/!p' file.txt

Appending lines

Append line after line 2

$ sed '2a Text after line 2' file.txt

Append line at the end of the file

$ sed '$a THE END!' file.txt

Append line after every 3rd line starting from line 3

$ sed '3~3a Some text' file.txt

Numbering

Number line of a file (simple left alignment)

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

Number line of a file (number on left, right-aligned)

$ sed = file.txt | sed 'N; s/^/   /; s/ *\(.\{6,\}\)\n/\1  /'

Number line of file, but only print numbers if line is not blank

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

Count lines (emulates “wc -l”)

$ sed -n '$='

Prepending lines

Insert text before line 5

$ sed '5i line number five' file.txt

Insert “Example: “ before each line that contains “hello”

$ sed '/hello/i Example: ' file.txt

Deleting lines

Delete line 5-7 in file

$ sed '5,7d' file.txt

Delete every 2nd line starting with line 3

$ sed '3~2d' file.txt

Delete the last line in file

$ sed '$d' file.txt

Delete lines starting with “Hello”

$ sed '/^Hello/d' file.txt

Delete all empty lines

$ sed '/^$/d' file.txt

Delete lines starting with “#”

$ sed '/^#/d' file.txt

File spacing

Double space

$ sed G

Delete all blank lines and double space

$ sed '/^$/d;G'

Triple space a file

$ sed 'G;G'

Undo double-spacing

$ sed 'n;d'

Insert a blank line above line which matches “regex”

$ sed '/regex/{x;p;x;}'

Insert a blank line below line which matches “regex”

$ sed '/regex/G'

Insert a blank line around line which matches “regex”

$ sed '/regex/{x;p;x;G;}'

sed