Lord Sed

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Table of Contents

What is SED?

Sed short for stream editor. It reads input line by line, applies commands and output the results.

  • find and replace text
  • delete lines
  • insert/append text
  • extract specific lines
  • batch editing files

Edit and Save

First we must discuss that in default behavior sed don’t save the output to the file. Below are some of the common method to ssave to the file.

Save to a new file

This is the recommended method, for safety.

1sed 's/old/new/g' file.txt > new.txt

Overwrite the original - in-place editing

If you are sure what you are doing.

1sed -i 's/old/new/g' file.txt

Print

1sed '' file.txt
2
3Hello World!
4hello world!
5Hello World!
6Dunk it Jonathan!
7Nagrigat agbiyag ditoy lubong.
8I love you MOM!

1sed -n '4p' file.txt
2
3Dunk it Jonathan!

1sed -n '3,6p' file.txt
2
3Hello World!
4Dunk it Jonathan!
5Nagrigat agbiyag ditoy lubong.
6I love you MOM!

1sed -n '/I/p' file.txt
2
3I love you MOM!

Find and Replace

Replace first match

1sed 's/Hello/Goodbye/' file.txt
2
3Goodbye World!
4hello world!
5Goodbye World!
6Dunk it Jonathan!
7Nagrigat agbiyag ditoy lubong.
8I love you MOM!

Replace all matches

1sed 's/World/Hell/g' file.txt
2
3Hello Hell!
4hello world!
5Hello Hell!
6Dunk it Jonathan!
7Nagrigat agbiyag ditoy lubong.
8I love you MOM!

Case sensitive replace

1sed 's/Hello/Goodbye/gi' file.txt
2
3Goodbye World!
4Goodbye world!
5Goodbye World!
6Dunk it Jonathan!
7Nagrigat agbiyag ditoy lubong.
8I love you MOM!

Replace only on specific line

1sed '3s/Hello/Goodbye/' file.txt
2
3Hello World!
4hello world!
5Goodbye World!
6Dunk it Jonathan!
7Nagrigat agbiyag ditoy lubong.
8I love you MOM!

Delete

Delete a word

This is the same with replace, just set it to blank.

1sed 's/Dunk//g' file.txt
2
3Hello World!
4hello world!
5Hello World!
6 it Jonathan!
7Nagrigat agbiyag ditoy lubong.
8I love you MOM!

Delete a line

1sed '5d' file.txt
2
3Hello World!
4hello world!
5Hello World!
6Dunk it Jonathan!
7I love you MOM!

Delete Range

1sed '2,6d' file.txt
2
3Hello World!

Delete matching line

1sed '/I/d' file.txt
2
3Hello World!
4hello world!
5Hello World!
6Dunk it Jonathan!
7Nagrigat agbiyag ditoy lubong.

Insert and Appending

Insert before a line

1sed '2i Hey let me in!' file.txt
2
3Hello World!
4Hey let me in!
5hello world!
6Hello World!
7Dunk it Jonathan!
8Nagrigat agbiyag ditoy lubong.
9I love you MOM!

Append after a lin

1sed '3a Dunk it Jonathan!' file.txt
2
3Hello World!
4hello world!
5Hello World!
6Dunk it Jonathan!
7Dunk it Jonathan!
8Nagrigat agbiyag ditoy lubong.
9I love you MOM!

Insert before match

1sed '/Dunk/i Lalaland' file.txt
2
3Hello World!
4hello world!
5Hello World!
6Lalaland
7Dunk it Jonathan!
8Nagrigat agbiyag ditoy lubong.
9I love you MOM!

Regex

Let’s first change the content of file.txt to better demostrate regex. file.txt

1Hello World!
2hello world!
3<pusa>
41 2 3 takbo...
5pelepens; flood control;
6Dunk it Jonathan!

Word boundary match

1sed 's/\<pusa\>/aso/g' file.txt
2
3Hello World!
4hello world!
5<aso>
61 2 3 takbo...
7pelepens; flood control;
8Dunk it Jonathan!

Replace Number

1sed 's/[0-2]\+/baliw/g' file.txt
2
3Hello World!
4hello world!
5<pusa>
6baliw baliw 3 takbo...
7pelepens; flood control;
8Dunk it Jonathan!

Capture groups

1sed 's/\(hello\) \(world\)/\2, \1/gi' file.txt
2
3World, Hello!
4world, hello!
5<pusa>
61 2 3 takbo...
7pelepens; flood control;
8Dunk it Jonathan!

Multiple Commands

1sed -e 's/Dunk/Shoot/' -e 's/takbo/talon/' file.txt
2
3Hello World!
4hello world!
5<pusa>
61 2 3 talon...
7pelepens; flood control;
8Shoot it Jonathan!

Using semicolon

1sed -e 's/Dunk/Shoot/; s/takbo/talon/' file.txt
2
3Hello World!
4hello world!
5<pusa>
61 2 3 talon...
7pelepens; flood control;
8Shoot it Jonathan!

Conditional Execution

Run command only on matching line

1sed '/orld/s/Hello/bubble gum/gi' file.txt
2
3bubble gum World!
4bubble gum world!
5<pusa>
61 2 3 takbo...
7pelepens; flood control;
8Dunk it Jonathan!

Real world example

Removing blank lines

1sed '/^$/d'

Remove trailing spaces

1sed 's/[ \t]*$//'

Number lines

1sed '=' file.txt | sed 'N;s/\n/ /'
2
31 Hello World!
42 hello world!
53 <pusa>
64 1 2 3 takbo...
75 pelepens; flood control;
86 Dunk it Jonathan!

Extract between two patterns

1sed -n '/1/,/flood/p' file.txt
2
31 2 3 takbo...
4pelepens; flood control;

Scripts

Create file script.sed.

1s/hello/world/g
2s/\<pusa\>/aso/g

Run.

1sed -f script.sed file.txt
2
3Hello World!
4world world!
5<aso>
61 2 3 takbo...
7pelepens; flood control;
8Dunk it Jonathan!