---
title: "sed command"
description: "In this tutorial: Command structure Commands Examples Sed (short for 'stream' 'editor' is a special editor that is used for modifying files automatically. It is not an interactive editor, so it can..."
url: https://www.inmotionhosting.com/support/server/linux/sed/
date: 2014-11-11
modified: 2014-11-11
author: "Scott Mitchell"
categories: ["Linux"]
type: post
lang: en
---

# sed command

## In this tutorial:

[Command structure](#structure) [Commands](#commands) [Examples](#examples) *Sed* (short for '**s**tream' '**ed**itor' is a special editor that is used for modifying files automatically. It is not an interactive editor, so it can be used if you are wanting to write a program to make changes in a file. Follow along below as we go through several examples of the *sed* command.

## Command Structure

**Command: **sed
**Synopsis: **sed ... {script-only-if-there-is-no-other-script} ...

**List of Options: ** **NOTE:** Some options have only a short name, some only a long name, and some both. If an option has both, then you may use either format.

| Short Name | Long name | Description |
| --- | --- | --- |
| -n | --quiet --silent | This is quiet mode, where it does not print out anything unless a specific print request exists. |
| -e script | --expression=script | Add the script to the commands to be executed. |
| -f *script-file* | --file=*script-file* | This adds the contents of the 'script-file' to the commands to be executed |
| | --follow-symlinks | Follows symlinks when processing. The hard links will still be broken. |
| -i | --in-place[=SUFFIX] | This will edit the files in place and make backups if an extension is supplied. |
| -c | --copy | This is used when shuffling files using the *-i* option. It avoids breaking links, both hard and symlinks. *--follow-symlinks* is usually a better option, however, as it is both more secure and faster. |
| -l N | --line-length=N | Use this command to specify thelength of a line, N, before it wraps. |
| | --posix | THis disables al the GNU extensions. |
| -r | --regexp-extended | Command to use extended regular expressions in the script. |
| -s | --separate | Consider each file separately as opposed to one long stream. |
| -u | --unbuffered | Load minimal amounts of data form the input files and flus the output buffers more often. |
| | --version | Prints out the version information |

## List of Commands

| Structure | Description |
| --- | --- |
| = | Used to print line numbers where the supplied parameter is found. |
| a \*text* | Append text. This command inserts a new line and any specified text AFTER the specified parameter. |
| c \*text* | This command is used to find the line the specified parameter is on and then change it to the text provided. |
| i \*text* | Insert text. This command inserts a new line and any specified text BEFORE the specified parameter. |
| s /regexp/replacement | This looks through the file looking to match the *regexp* parameter. Once found, it replaces it with the *replacement* parameter. |

## Examples

Using the commands and options above, you can create many different combinations to tailor *sed* to filter your files. Below are several examples using the command and options.

### Substitution with sed s

This is one of the most often used options. This example below uses *sed* to look through a file named *old.txt* and substitute the word 'day' for 'night', saving the result to a file named 'new.txt.' # sed 's/day/night/' old.txt > new.txt When we *cat* the original 'old.txt' file, you can see it has two words.

# cat old.txt day night After running our command, when we *cat* the 'new.txt' file, you can see the word 'day' has been replaced with 'night'.

# cat new.txt night night

### Changing the delimiter for the s command

When using the *s* command in the example above, we preceded the parameters with a forward slash /. This works fine in many cases, but if you are wanting to use filepaths in your parameters, you may want to choose a different delimiter. To do this, simply precede the first parameter with your chosen parameter. For example, below we want to change the apth */home/userna5/public_html* to */home/userna5/public_html/testfolder*.

You could still use the slash delimiter, but you would need to escape all the slashes in your path, so it would end up looking like this: # sed '/\/home\/userna5\/public_html/\/home\/userna5\/public_html\/testfolder/' old.txt > new.txt This is quite ugly and can be confusing when trying to read it.

Now, by using a different delimiter, it is much easier to read. Below we display delimiters using a colon : and a pipe |. These are also commonly used delimiters. # sed ':/home/userna5/public_html:/home/userna5/public_html/testfolder:' old.txt > new.txt # sed '|/home/userna5/public_html|/home/userna5/public_html/testfolder|' old.txt > new.txt

### Adding a line with the a command

If you want to insert some information on a new line, you can do so with the '*a*' command. Here we want to add a new line with the sentence 'This is new' after the word 'day' from the 'old.txt' file and save it as 'new.txt.'

# sed '/day/ a\This is new' old.txt > new.txt When we nano the 'new.txt' file, we see the newly added content was inserted correctly. # cat new.txt day This is new night

### Changing a line with the c command

Rather than inserting a line, you can also change an existing line using the *c* command. In the example below, we use *sed* to change a line with the number 2 in it to say 'ne new new!'. You do need to be careful because as you notice, it also changed the lines numbered 12 and 20 because they also had a 2 in them. *Sed* can be pretty greedy and make changes whenever possible, so be as accurate as you can when specifying what to change.

# sed '/2/ c\new new new!' old.txt > new.txt # cat new.txt 1 day new new new! 3 4 5 6 7 8 9 10 11 new new new! 13 14 15 16 17 18 19 new new new!

### Finding the line number for a parameter using =

You can use *sed* to find the line number for a given parameter. For example, if I want to search a file named 'new.txt' for the word 'new', it would return a list of line numbers that contain that word. In the example below, we also use the option *-n* so that it only prints out the line numbers involved. # sed -n '/new/ =' new.txt 2 12 20 As you can see, the word new was found on lines 2, 12, and 20.