---
title: Sed
date: 2020-12-27 18:34:08
background: bg-red-400
tags:
- editor
- replace
- text
- utility
categories:
- Linux Command
intro: |
[Sed](https://www.gnu.org/software/sed/manual/sed.html) is a stream editor, this sed cheat sheet contains sed commands and some common sed tricks.
plugins:
- copyCode
---
## Getting Started
### Sed Usage
Syntax
```shell script
$ sed [options] command [input-file]
```
With pipeline
```shell script
$ cat report.txt | sed 's/Nick/John/g'
```
```shell script
$ echo '123abc' | sed 's/[0-9]+//g'
```
### Option Examples {.col-span-2}
| 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 |
{.show-header}
### Multiple commands
```shell script {.wrap}
$ 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
```shell 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
```shell script
$ 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-examples)
## Sed commands
### Commands {.col-span-2}
| 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 |
{.show-header}
### 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 |
See also: [File spacing](#file-spacing)
### Flags
```shell script
$ 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 {.row-span-2}
Replace all occurrences of a string
```shell script
$ sed 's/old/new/g' file.txt
```
Replace only the nth occurrence of a string
```shell script
$ sed 's/old/new/2' file.txt
```
Replace a string only on the 5th line
```shell script
$ sed '5 s/old/new/' file.txt
```
Replace "world" with "universe" but only if the line begins with "hello"
```shell script
$ sed '/hello/s/world/universe/' file.txt
```
Remove "\" from the end of each line
```shell script
$ sed 's/\\$//' file.txt
```
Remove all whitespace from beginning of each line
```shell script
$ sed 's/^\s*//' file.txt
```
Remove comments. Even those that are at the end of a line
```shell script
$ sed 's/#.*$//' file.txt
```
### Search for text
Search for a string and only print the lines that were matched
```shell script
$ sed -n '/hello/p' file.txt
```
Case insensitive search
```shell script
$ sed -n '/hello/Ip' file.txt
```
Search for a string but only output lines that do not match
```shell script
$ sed -n '/hello/!p' file.txt
```
### Appending lines
Append line after line 2
```shell script
$ sed '2a Text after line 2' file.txt
```
Append line at the end of the file
```shell script
$ sed '$a THE END!' file.txt
```
Append line after every 3rd line starting from line 3
```shell script
$ sed '3~3a Some text' file.txt
```
### Numbering {.col-span-2}
Number line of a file (simple left alignment)
```shell script
$ sed = file.txt | sed 'N;s/\n/\t/'
```
Number line of a file (number on left, right-aligned)
```shell script
$ sed = file.txt | sed 'N; s/^/ /; s/ *\(.\{6,\}\)\n/\1 /'
```
Number line of file, but only print numbers if line is not blank
```shell script
$ sed '/./=' file.txt | sed '/./N; s/\n/ /'
```
Count lines (emulates "wc -l")
```shell script
$ sed -n '$='
```
### Prepending lines
Insert text before line 5
```shell script
$ sed '5i line number five' file.txt
```
Insert "Example: " before each line that contains "hello"
```shell script
$ sed '/hello/i Example: ' file.txt
```
### Deleting lines
Delete line 5-7 in file
```shell script
$ sed '5,7d' file.txt
```
Delete every 2nd line starting with line 3
```shell script
$ sed '3~2d' file.txt
```
Delete the last line in file
```shell script
$ sed '$d' file.txt
```
Delete lines starting with "Hello"
```shell script
$ sed '/^Hello/d' file.txt
```
Delete all empty lines
```shell script
$ sed '/^$/d' file.txt
```
Delete lines starting with "#"
```shell script
$ sed '/^#/d' file.txt
```
### File spacing
Double space
```shell script
$ sed G
```
Delete all blank lines and double space
```shell script
$ sed '/^$/d;G'
```
Triple space a file
```shell script
$ sed 'G;G'
```
Undo double-spacing
```shell script
$ sed 'n;d'
```
Insert a blank line above line which matches "regex"
```shell script
$ sed '/regex/{x;p;x;}'
```
Insert a blank line below line which matches "regex"
```shell script
$ sed '/regex/G'
```
Insert a blank line around line which matches "regex"
```shell script
$ sed '/regex/{x;p;x;G;}'
```
## Also see {.cols-1}
- [sed cheatsheet](https://gist.github.com/ssstonebraker/6140154) _(gist.github.com)_