sed-command-examples.md

50 sed Command Examples

From 50 sed command examples

sed is a useful text processing feature of GNU/Linux. The full form of sed is Stream Editor. Many types of simple and complicated text processing tasks can be done very easily by using sed command. Any particular string in a text or a file can be searched, replaced and deleted by using regular expression with sed command. But this commands performs all types of modification temporarily and the original file content is not changed by default. The user can store the modified content into another file if needs. The basic uses of sed command are explained in this tutorial by using 50 unique examples.Before starting this tutorial you must check the installed version of sed in your operating system by running the following command. The tutorial is designed based on GNU sed. So this version of sed will be required to practice the examples shown in this tutorial.

$ sed --version

The following output shows that GNU Sed of version 4.4 is installed in the system.

Syntax:

sed [options]…  [script] [file]

If no filename is provided with sed command, then the script will work on standard input data. The sed script can be executed without any option.

Content:

• Basic text substitution using sed
• Replace all instances of a text in a particular line of a file by using g option
• Replace the second occurrence only of a match on each line
• Replace the last occurrence only of a match on each line
• Replace the first match in a file with new text
• Replace the last match in a file with new text Escaping backslash in replace commands to manage search and replace of - file paths
• Replace all files full path with just the filename no directory
• Substitute text but only if some other text is found in the string
• Substitute text but only if some other text is not found in the string
• Add string before after the matching pattern using \1
• Delete matching lines
• Delete matching line and 2 lines after matching line
• Delete all spaces at end of the line of text
• Delete all lines that have a match two times on the line
• Delete all lines that have the only whitespace
• Delete all non-printable characters
• If there is a match in line append something to end of line
• If there is a match in the line insert line before the match
• If there is a match in the line insert line after the match
• If there is not a match append something to the end of line
• If there is not a match delete the line
• Duplicate matched text after adding a space after the text
• Replace one of a list of strings with the new string
• Replace a matched string with a string that contains newlines
• Remove newlines from file and insert a comma at end of each line
• Remove commas and add newlines to split the text into multiple lines
• Find case insensitive match and delete line
• Find case insensitive match and replace with new text Find case insensitive match and replace with all uppercase of the same - text
• Find case insensitive match and replace with all lowercase of same text
• Replace all uppercase characters in text with lowercase characters
• Search for the number in line and append currency symbol after the number
• Add commas to numbers that have more than 3 digits
• Replace tab characters with 4 space characters
• Replace 4 consecutive space characters with a tab character
• Truncate all lines to first 80 characters
• Search for a string regex and append some standard text after it
• Search for a string regex and a second copy of found string after it
• Running multi-line sed scripts from a file
• Match a multi-line pattern and replace with new multi-line text
• Replace order of two words that match a pattern
• Use multiple sed commands from the command-line
• Combine sed with other commands
• Insert an empty line in a file
• Delete all alpha-numeric characters from each line of a file.
• Use & to match string
• Switch pair of words
• Capitalize the first character of each word
• Print line numbers of the file

Basic text substitution using sed

Any particular part of a text can be searched and replaced by using searching and replacing pattern by using sed command. In the following example, s indicates the search and replace task. The word Bash will be searched in the text, “Bash Scripting Language” and if the word exists in the text then it will be replaced by the word Perl.

$ echo "Bash Scripting Language" | sed 's/Bash/Perl/'

Output:

The word, Bash exists in the text. So the output is Perl Scripting Language.

Perl Scripting Language

sed command can be used to substitution any part of a file content also. Create a text file named weekday.txt with the following content.

weekday.txt

Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Sunday

The following command will search and replace the text Sunday , by the text Sunday is holiday.

$ cat weekday.txt
$ sed 's/Sunday/Sunday is holiday/' weekday.txt

Output:

Sunday exists in weekday.txt file and this word is replaced by the text, Sunday is holiday after executing the above sed command.

Monday 
Tuesday 
Wednesday 
Thursday 
Friday 
Saturday 
Sunday is holiday

Replace all instances of a text in a particular line of a file using g option

g option is used in sed command to replace all occurrences of matching pattern. Create a text file named python.txt with the following content to know the use of g option. This file contains the word. Python multiple times.

python.txt

Python is a very popular language.
Python is easy to use. Python is easy to learn.
Python is a cross-platform language

The following command will replace all occurrences of Python in the second line of the file, python.txt. Here, Python occurs two times in the second line.

$ cat python.txt
$ sed '2 s/Python/perl/g' python.txt

Output:

The following output will appear after running the script. Here, All occurrence of Python in the second line is replaced by Perl.

Python is a very popular language.
perl is easy to use. perl is easy to learn.
Python is a cross-platform language%  

Replace the second occurrence only of a match on each line

If any word appears multiple times in a file then the particular occurrence of the word in each line can be replaced by using sed command with the occurrence number. The following sed command will replace the second occurrence of the searching pattern in each line of the file, python.txt.

$ sed 's/Python/perl/g2' python.txt

Output:

Here, the searching text, Python appears two times in the second line only and it is replaced by the text, perl.

Python is a very popular language.
Python is easy to use. perl is easy to learn.
Python is a cross-platform language%  

Replace the last occurrence only of a match on each line

Create a text file named lang.txt with the following content.

lang.txt

Bash Programming Language.  Python Programming Language. Perl Programming Language.
Hypertext Markup Language.
Extensible Markup Language.

$ sed 's/\(.*\)Programming/\1Scripting/' lang.txt

The \1 refers to the characters captured by the escaped parentheses.

Read

Output:

Bash Programming Language. Python Programming Language. Perl Scripting Language.
Hypertext Markup Language.
Extensible Markup Language.

Replace the first match in a file with new text

The following command will replace only the first match of the searching pattern, Python by the text, perl. Here, 1 is used to match the first occurrence of the pattern.

$ cat python.txt
$ sed '1 s/Python/perl/' python.txt
# or without a space
$ sed '1s/Python/perl/' python.txt

Output:

Here. the first occurrence of Python in the first line is replaced by perl.

perl is a very popular language.
Python is easy to use. Python is easy to learn.
Python is a cross-platform language%   

Replace the last match in a file with new text

The following command will replace the last occurrence of the searching pattern, Python by the text, Bash. Here, $ symbol is used to match the last occurrence of the pattern.

$ cat python.txt
$ sed -e '$ s/Python/Bash/' python.txt
# or without a space
$ sed -e '$s/Python/Bash/' python.txt

Output:

Python is a very popular language.
Python is easy to use. Python is easy to learn.
Bash is a cross-platform language

Escaping backslash in replace commands to manage search and replace of file paths

It is necessary to escape the backslash in the file path for searching and replacing. The following command of sed will add backslash () in the file path.

$ echo /home/ubuntu/code/perl/add.pl | sed 's;/;\\/;g'

Output:

The file path, /home/ubuntu/code/perl/add.pl is provided as input in the sed command and

\/home\/ubuntu\/code\/perl\/add.pl

Replace all files full path with just the filename no directory

The filename can be retrieved from the file path very easily by using basename command. sed command can also be used to retrieve the filename from the file path. The following command will retrieve the filename only from the file path provided by echo command.

$ echo "/home/ubuntu/temp/myfile.txt" | sed 's/.*\///'

Output:

Here, the filename, myfile.txt is printed as output.

myfile.txt

Substitute text but only if some other text is found in the string

Create a file named dept.txt with the following content to replace any text based on other text.

dept.txt

List of Total Students:

CSE - Count
EEE - Count
Civil - Count

Two replace commands are used in the following sed command. Here, the text, Count will be replaced by 100 in the line that contains the text, CSE and the text, Count will be replaced by 70 in the line that contains the searching pattern, EEE.

$ cat dept.txt
$ sed  -e '/CSE/ s/Count/100/; /EEE/ s/Count/70/;' dept.txt

Output:

The following output will appear after the running the above commands.

CSE - Count
EEE - Count
Civil - Count 

CSE - 100
EEE - 70
Civil - Count 

Substitute text but only if some other text is not found in the string

The following sed command will replace the Count value in the line that does not contain the text, CSE. dept.txt file contains two lines that do not contain the text, CSE. So, the Count text will be replaced by 80 in two lines.

$ cat dept.txt
$ sed -i -e '/CSE/! s/Count/80/;' dept.txt

Output:

CSE - Count
EEE - 80
Civil - 80

Add string before and after the matching pattern using \1

The sequence of matching patterns of sed command is denoted by \1, \2 and so on. The following sed command will search the pattern, Bash and if the pattern matches then it will be accessed by \1′ in the part of replacing text. Here, the text, Bashis searched in the input text and, one text is added before and another text is added after\1`.

$ echo "Bash language" | sed  's/\(Bash\)/Learn \1 programming/'

Output:

Here, Learn text is added before Bash and programming text is added after Bash.

Learn Bash programming language

Delete matching lines

d option is used in sed command to delete any line from the file. Create a file named os.txt and add the following content to test the function of d option.

cat os.txt

Windows
Linux
Android
OS

The following sed command will delete those lines from os.txt file that contains the text, OS.

$ cat os.txt
$ sed '/OS/d' os.txt

Output:

Windows
Linux
Android

Delete matching line and 2 lines after matching line

The following command will delete three lines from the file os.txt if the pattern, Linux is found. os.txt contains the text, Linux in the second line. So, this line and the next two lines will be deleted.

$ sed '/Linux/,+2d' os.txt

Output:

Windows

Delete all spaces at end of the line of text

Using [:blank:] class can be used to remove spaces and tabs from the text or the content of any file. The following command will remove the spaces at the end of each line of the file, os.txt.

$ cat os.txt
$ sed 's/[[:blank:]]*$//' os.txt

Output:

os.txt contains empty lines after each line those are deleted by the above sed command.

Windows
Linux
Android
OS

Delete all lines that have a match two times on the line

Create a text file named, input.txt with the following content and delete those lines of the file that contains the searching pattern two times.

input.txt

PHP is a server-side scripting language.
PHP is an open-source language and PHP is case-sensitive.
PHP is platform-independent.

PHP text contains two times in the second line of the file, input.txt. Two sed commands are used in this example to remove those lines that contain the pattern php two times. The first sed command will replace the second occurrence of php in each line by dl and send the output into the second sed command as input. The second sed command will delete those lines that contain the text, dl.

$ cat input.txt
$ sed  's/php/dl/i2;t' input.txt | sed '/dl/d'

Output:

input.txt file has two lines that contain the pattern, php two times. So,

PHP is a server-side scripting language.
PHP is platform-independent.

Delete all lines that have only white-space

Select any file that contains empty lines in the content to test this example. input.txt file that is created in the previous example, contains two empty lines that can be deleted by using the following sed command. Here, ^$ is used to find out the empty lines in the file, input.txt.

$ cat input.txt
$ sed '/^$/d' input.txt

Output:

PHP is a server-side scripting language.
PHP is an open-source language and PHP is case-sensitive.
PHP is platform-independent.

Delete all non-printable characters

Non-printable characters can be deleted from any text by replacing non-printable characters by none. [:print:] class is used in this example to find out the non-printable characters. \t is a non-printable character and it cant be parsed directly by the echocommand. For this,\tcharacter is assigned in a variable, $tab that is used in anechocommand. The output of theechocommand is sent in thesedcommand that will remove the character,\t` from the output.

$ tab=$'\t'
$ echo "Hello$tabWorld"
$ echo "Hello$tabWorld" | sed 's/[^[:print:]]//g'

Output:

The first echo command will print the output with tab space and the sed command will print the output after removing the tab space.

Hello

If there is a match in line append something to end of line

The following command will append 10 at the end of the line that contains the text, Windows in the os.txt file.

$ cat os.txt
$ sed '/Windows/ s/$/ 10/' os.txt

Output:

Windows 10
Linux
Android
OS

If there is a match in the line insert a line before the text

The following sed command will search the text, PHP is platform-independent in the input.txt file that is created before. If the file contains this text in any line then, PHP is an interpreted language will be inserted before that line.

$ cat input.txt
$ sed '/PHP is platform-independent/ s/^/PHP is an interpreted language.\n/' input.txt

Output:

PHP is a server-side scripting language.
PHP is an open-source language and PHP is case-sensitive.
PHP is an interpreted language.
PHP is platform-independent.

If there is a match in the line insert a line after that line

The following sed command will search the text, Linux in the file os.txt and if the text exists in any line then a new text, Ubuntu will be inserted after that line.

$ cat os.txt
$ sed 's/Linux/&\nUbuntu/' os.txt

Output:

Windows 
Linux
Ubuntu 
Android 
OS 

If there is not a match append something to the end of line

NOT WORKING

The following sed command will search those lines in os.txt that does not contain the text, Linux and append the text, Operating System at the end of each line. Here, $ symbol is used to identify the line where the new text will be appended.

$ cat os.txt
$ sed '/Linux/! S/$/ Operating System/' os.txt

Output:

Three lines exist in the file os.txt that does not contain the text, Linux and the new text s added at the end of these lines.

Not working error: sed: -e expression #1, char 10: unknown command: S

If there is not a match delete the line

Create a file named web.txt and add the following content and delete lines that do not contain the matching pattern. web.txt HTML 5JavaScriptCSSPHPMySQLJQuery The following sed command will search and delete those lines that do not contain the text, CSS. $ cat web.txt$ sed /CSS/!d web.txt Output: There is one line exists in the file that contains the text, CSE. So, the output contains just one line.

Duplicate matched text after adding a space after the text

The following sed command will search the word, to in the file, python.txt and if the word exists then the same word will be inserted after the search word by adding space. Here, & symbol is used to append the duplicate text.

$ cat python.txt
$ sed -e 's/to /& to/g' python.txt

Output:

The following output will appear after running the commands. Here, the word, to is searched in the file, python.txt and this word exists in the second line of this file. So, to with space is added after the matching text.

Python is a very popular language.
Python is easy to  touse. Python is easy to  tolearn.
Python is a cross-platform language

Replace one list of strings with the new string

You have to create two list files for testing this example. Create a text file named list1.txt and add the following content.

list1.txt

1001 => Jafar Ali
1023 => Nir Hossain
1067 => John Michel

Create a text file named list2.txt and add the following content.

list2.txt

1001    CSE     GPA-3.63
1002    CSE     GPA-3.24
1023    CSE     GPA-3.11
1067    CSE     GPA-3.84

The following sed command will match the first column of the two text files shown above and replace the matching text with the value of the third column of the file list1.txt.

$ cat list1.txt
$ cat list2.txt
$ sed `cat list1.txt | awk '{print "-e s/"$1"/"$3"/"}'`<<<"` cat list2.txt`"

Output:

1001, 1023 and 1067 of list1.txt file match with the three data of list2.txt file and these values are replaced by corresponding names of the third column of list1.txt.

Jafar    CSE     GPA-3.63
1002    CSE     GPA-3.24
Nir    CSE     GPA-3.11
John    CSE     GPA-3.84

Replace the matched string with a string that contains newlines

The following command will take input from the echo command and search the word, Python in the text. If the word exists in the text then a new text, Added Text will be inserted with newline.

echo "Bash Perl Python Java PHP ASP" | sed 's/Python/Added Text\n/' 

Output:

Bash Perl Added Text
 Java PHP ASP

Remove newlines from file and insert a comma at end of each line

The following sed command will replace each newline by a comma in the file os.txt. Here, -z option is used to separate the line by NULL character.

$ sed -z 's/\n/,/g' os.txt

Output:

Windows,Linux,Android,OS,Linux2

Remove commas and add newline to split the text into multiple lines

The following sed command will take the comma-separated line from the echo command as input and replace the comma by newline.

$ echo "Kaniz Fatema,30th,batch" | sed "s/,/\n/g"

Output:

The input text contains three comma-separated data that are replaced by newline and printed in three lines.

Kaniz Fatema
30th
batch

Find case insensitive match and delete line

I is used in sed command for the case-insensitive match that indicates ignore case. The following sed command will search the line that contains the word, linux and delete the line from os.txt file.

$ cat os.txt
$ sed '/linux/Id' os.txt

Output:

os.txt contains the word, Linux that matched with the pattern, linux for case-insensitive search and deleted.

Windows
Android
OS

Find case insensitive match and replace with new text

The following sed command will take the input from the echo command and replace the word, bash by the word, PHP.

$ echo "I like bash programming " | sed 's/Bash/PHP/i'

Output:

Here, the word, Bash matched with the word, bash for case-insensitive search and replaced by the word, PHP.

I like PHP programming 

Find case insensitive match and replace with all uppercase of the same text

\U is used in sed to convert any text to all uppercase letter. The following sed command will search the word, linux in the os.txt file and if the word exists then it will replace the word with all uppercase letters.

$ cat os.txt
$ sed 's/\(linux\)/\U\1/Ig' os.txt

Output:

The word, Linux of os.txt file is replaced by the word, LINUX.

Windows
LINUX
Android
OS
LINUX2

Find case insensitive match and replace with all lowercase of same text

\L is used in sed to convert any text to all lowercase letters. The following sed command will search the word, Linux in the os.txt file and replace the word by all lowercase letters.

$ cat os.txt
$ sed 's/\(linux\)/\L\1/Ig' os.txt

Output:

The word, Linux is replaced by the word, linux here.

Windows
linux
Android
OS
linux2

Replace all uppercase characters of the text with lowercase characters

The following sed command will search all uppercase characters in the os.txt file and replace the characters by lowercase letters by using \L.

$ cat os.txt
$ sed  's/\(.*\)/\L\1/' os.txt

Output:

windows
linux
android
os
linux2

Search for number in line and append any currency symbol before the number

NOT WORKING

Create a file named items.txt with the following content.

items.txt

HDD       100
Monitor   80
Mouse     10

The following sed command will search the number in each line of items.txt file and append the currency symbol, $ before each number.

$ cat items.txt
$ sed 's/\([0-9]\)/$\1/g' items.txt

Output:

Here, $ symbol is added before the number of each line.

HDD       $1$0$0
Monitor   $8$0
Mouse     $1$0%  

Add commas to numbers that have more than 3 digits

The following sed command will take a number as input from echo command and add comma after each group of three digits counting from the right. Here, :a indicates the label and ta is used to iterate grouping process.

$ echo "5098673" | sed -e :a -e 's/\(.*[0-9]\)\([0-9]\{3\}\)/\1,\2/;ta'

Output:

The number 5098673 is given in the echo command and the sed command generated the number 5,098,673 by adding comma after each group of three digits.

5,098,673

Replaces tab character with 4 space characters

The following sed command will replace each tab (\t) character by four space characters. $ symbol is used in the sed command to match the tab character and g is used to replace all tab characters.

$ echo -e "1\t2\t3" | sed $'s/\t/    /g'

Output:

1    2    3

Replaces 4 consecutive space characters with tab character

The following command will replace 4 consecutive characters with tab (\t) character.

$ echo -e "1    2" | sed $'s/    /\t/g'

Output:

1       2

Truncate all lines to first 80 characters

Create a text file named in.txt that contains the lines more than 80 characters to test this example.

in.txt

PHP is a server-side scripting language.
PHP is an open-source language and PHP is case-sensitive. PHP is platform-independent.

The following sed command will truncate each line of in.txt file into 80 characters.

$ cat in.txt
$ sed 's/\(^.\{1,80\}\).*/\1/' in.txt

Output:

The second line of in.txt file contains more than 80 characters and this line is truncated in the output.

PHP is a server-side scripting language.
PHP is an open-source language and PHP is case-sensitive. PHP is platform-indepe

Search for a string regex and append some standard text after it

The following sed command will search the text, hello in the input text and append the text, John after that text.

$ echo "hello, how are you?" | sed 's/\(hello\)/\1 John/'

Output:

hello John, how are you?

Search for string regex and append some text after the second match in each line

The following sed command will search the text, PHP in each line of input.txt and replace the second match in each line with the text, New Text Added.

$ cat input.txt
$ sed 's/\(PHP\)/\1 (New Text added)/2' input.txt

Output:

The searching text, PHP appears for two times in the second and third lines of input.txt file. So, the text, New Text added is inserted in the second and third lines.

PHP is a server-side scripting language.
PHP is an open-source language and PHP (New Text added) is case-sensitive.
PHP is platform-independent.

Running multi-line sed scripts from a file

Multiple sed scripts can be stored in a file and all the scripts can be executed together by running sed command. Create a file named sedcmd and add the following content. Here, two sed scripts are added in the file. One script will replace the text, PHP by ASP another script will replace the text, independent by the text, dependent.

sedcmd

s/PHP/ASP/
s/independent/dependent/

The following sed command will replace all PHP and independent text by ASP and dependent. Here, -f option is used in the sed command to execute sed script from the file.

$ cat sedcmd
$ sed -f sedcmd  input.txt

Output:

The following output will appear after running above commands.

ASP is a server-side scripting language.
ASP is an open-source language and PHP is case-sensitive.
ASP is platform-dependent.

Match a multi-line pattern and replace with new multi-line text

NOT WORKING

The following sed command will search the multi-line text, Linux\nAndroid and if the pattern matches then the matching lines will be replaced by the multi-line text, Ubuntu\nAndroid Lollipop. Here, P and D are used for multiline processing.

$ cat os.txt
$ sed '$!N;s/Linux\nAndoid/Ubuntu\nAndoid Lollipop/;P;D' os.txt

Output:

Replace order of two words in a text that match a pattern

The following sed command will take the input of two words from echo command and replace the order of these words.

$ echo "perl python" | sed -e 's/\([^ ]*\) *\([^ ]*\)/\2 \1/'
$ sed -e 's/\([^ ]*\) *\([^ ]*\)/\2 \1/' course.txt

Output:

python perl

ASP PHP
Oracle MySQL
Laravel CodeIgniter

Execute multiple sed commands from the command-line

-e option is used in sed command to run multiple sed scripts from the command line. The following sed command will take a text as input from echo command and replaces Ubuntu by Kubuntu and Centos by Fedora.

$ echo "Ubuntu Centos Debian" | sed -e 's/Ubuntu/Kubuntu/; s/Centos/Fedora/'

Output:

Here, Ubuntu and Centos are replaced by Kubuntu and Fedora.

Kubuntu Fedora Debian

Combine sed with other commands

The following command will combine the sed command with cat command. The first sed command will take input from os.txt file and send the output of the command to second sed command after replacing the text LinuxbyFedora. The second sedcommand will replace the text,WindowsbyWindows 10`.

$ cat os.txt | sed 's/Linux/Fedora/'| sed 's/windows/Windows 10/i'

Output:

Windows 10 
Fedora 
Android 
OS        
Fedora2

Insert empty line in a file

Create a file named stdlist with the following content.

stdlist

#ID     #Name
[101]   -Ali
[102]   -Neha

G option is used to insert empty line in a file. The following sed command will insert empty lines after each line of stdlist file.

$ cat stdlist
$ sed G stdlist

Output:

An empty line is inserted after each line of the file.

#ID     #Name

[101]   -Ali

[102]   -Neha

Replace all alpha-numeric characters by space in each line of a file.

The following command will replace all alpha-numeric characters by space in the stdlist file.

$ cat stdlist
$ sed 's/[A-Za-z0-9]//g' stdlist

Output:

#     #
[]   -
[]   -

Use & to print matched string

The following command will search the word starting with L and replace the text by appending Matched String is – with the matched word by using & symbol. Here, p is used to print the modified text.

$ sed -n 's/^L/Matched String is - &/p' os.txt

Output:

Matched String is - Linux 

Switch pair of words in a file

Create a text file named course.txt with the following content that contains the pair of words in each line.

course.txt

PHP            ASP
MySQL          Oracle
CodeIgniter    Laravel

The following command will switch the pair of words in each line of the file, course.txt.

$ sed  's/\([^ ]*\) *\([^ ]*\)/\2 \1/' course.txt

Output:

The following output will appear after switching the pair of words in each line.

ASP PHP
Oracle MySQL
Laravel CodeIgniter

Capitalize the first character of each word

The following sed command will take input text from the echo command and convert the first character of each word to a capital letter.

$ echo "I like bash programming" | sed 's/\([a-z]\)\([a-zA-Z0-9]*\)/\u\1\2/g'

Output:

The input text, “I like bash programming” is printed as “I Like Bash Programming” after capitalizing the first word.

I Like Bash Programming

Print line numbers of the file

= symbol is used sed command to print the line number before each line of a file. The following command will print the content of os.txt file with line number.

$ sed '=' os.txt

Output:

There are four lines in os.txt file. So, the line number is printed before each line of the file.

1
Windows 
2
Linux 
3
Android 
4
OS  

Conclusion:

Different uses of sed command are explained in this tutorial by using very simple examples. The output of all sed scripts mentioned here are generated temporary and the content of the original file remained unchanged. But if you want you can modify the original file by using –i or –in-place option of sed command. If you are a new Linux user and want to learn the basic uses of sedcommand to perform various types of string manipulation tasks, then this tutorial will help you. After reading this tutorial, hope, any user will get the clear concept about the functions ofsed` command.

Frequently Asked Questions What is the sed command used for? The sed command has a number of different uses. That being said, the main usage is for substituting words in a file, or finding and replacing.

The great thing about sed is that you can search for a word in a file and replace it, but you never even have to open the file – sed just does it all for you!

As well as this, it can be used for deletion. All you need to do is type the word you want to find, replace or delete into sed, and it brings it up for you – you can then choose to replace that word or delete all traces of the word from your file.

sed is a fantastic tool to be able to replace things like IP addresses and anything that is highly sensitive that you would not otherwise want to put in a file. sed is a must-know for any software engineer!

What is S and G in sed command? In its most simple terms, the S function that can be used in sed simply means substitute. After typing the S you can replace or substitute anything you wish – just typing S will only replace the first occurrence of the word on a line.

Therefore, if you have a sentence or line that mentions it more than once, the S function is not ideal as it will only substitute the first occurrence. You can specify a pattern to make S replace words every two occurrences as well.

Specifying G at the end of the sed command will do a global replacement (that is what the G stands for). With this in mind, if you specify G it will replace every occurrence of the word you have chosen, rather than just the first occurrence that the S does.

How do I run a sed script? You can run a sed script in a number of ways but the most common is on the command line. Here you can just specify sed and the file you want to use the command on.

This allows you to use sed on that file, allowing you to find, delete and substitute as needed.

You can also use it in a shell script, and this way you can pass whatever you want to the script, and it will run the find and replace command for you. This is useful for not wanting to specify highly sensitive data inside a script, so instead, you can pass it in as a variable

Bear in mind that this is of course only available on Linux, and so you will need to ensure you have a Linux command line in order to run your sed script.