If you are working or using unix operating system, then you
must be proficient in sed language. Sed command in unix is very helpful for manipulation of file. While writing this article, I am considering this you are aware about the sed’s
little basics. Sed is a great utility which solves complex tasks by few lines
of code.
Sed stands for Stream
Editor. It is very powerful command to file manipulatation, filter lines
while reading file and transform text. Sed works both the way i.e. Sed can read
file and do operations on it or Sed can take inputs from pipe. If you are new learner then you will face
difficulty to understand the sed command but once you understood then It will
be easier to use as you need.
We are going to use below file in all 10 examples.
root@hello:~/test# cat salary.txt
1001,Ajay,Manager,25000
101,Satish,Founder,30000
302,Atul,CEO,26000
434,Raj,Senior Manager, 26000
1231,Kalyan,Human Resource,20000
|
The above salary database contains the columns as
- Employee ID
- Name
- Designation
- Salary
Basic Syntax of sed
command:
sed [options] {sed-commands}
{input-file}
sed [options] -e {sed-command-1} -e
{sed-command-2}{input-file}
|
Sed reads one line at a time from input file and executes
sed - command on that particular line. If we want to execute multiple commands
in a single line using several –e arguments, you can split them into multiple
lines using a backslash as below:
sed -n \
-e '/^mysql/ p' \
-e '/^other/ p' \
/etc/groups
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10 special tricks of Sed as follows :
1. Print the lines of input file after specific interval i.e. print 1st, 3rd, 5th line of file. Operator ~ used in an address range. Its special meaning is to skip lines between commands. Below command you can use to print the odd numbered lines or to print the even numbered lines.
root@hello:~/test# sed -n '1~2 p' salary.txt
1001,Ajay,Manager,25000
302,Atul,CEO,26000
1231,Kalyan,Human Resource,20000
|
2. Print the lines matching with keyword.
root@hello:~/test# sed -n '/Atul/p' salary.txt
302,Atul,CEO,26000
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3. Print the lines matching with keyword and 2 lines immediately after that. i.e. If matched keyword found then print 3 lines including matched keyword line and 2 lines immediately after that line.
root@hello:~/test# sed -n
'/Atul/, +2p' salary.txt
302,Atul,CEO,26000
434,Raj,Senior Manager, 26000
1231,Kalyan,Human
Resource,20000
|
You can use above command for deleting lines in output by
using “d” instead of “p” option. i.e. if you want to delete lines starting from
1st match of “Atul” keyword till 4th line of file then
you can use it as
sed '/Atul/,4 d' salary.txt
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4. Write the content of salary.txt file to new_salary.txt file. i.e. simple copy the salary.txt file into new_salary.txt file.
root@hello:~/test# sed 'w
new_salary.txt' salary.txt
1001,Ajay,Manager,25000
101,Satish,Founder,30000
302,Atul,CEO,26000
434,Raj,Senior Manager, 26000
1231,Kalyan,Human
Resource,20000
root@hello:~/test#
root@hello:~/test# cat
new_salary.txt
1001,Ajay,Manager,25000
101,Satish,Founder,30000
302,Atul,CEO,26000
434,Raj,Senior Manager, 26000
1231,Kalyan,Human
Resource,20000
root@hello:~/test#
|
5. Write the lines matching pattern “Atul” to pattern_found.txt file. Below command can be used for write only odd numbered line (1~2) or write only even numbered lines (2~2).
root@ctier:~/test# sed -n
'/Atul/ w pattern_found.txt' salary.txt
root@ctier:~/test# cat
pattern_found.txt
302,Atul,CEO,26000
root@ctier:~/test#
|
You
can all above commands by replacing “p” or “d” by “w” option.
Want to know more about : How to run Windows softwares on Linux
|
6. Mostly, sed used to substitute pattern by another pattern.
sed
'[address-range|pattern-range] s/originalstring/replacement-string/[substitute-flags]'
inputfile
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Replace all occurrences of Atul with Mohan:
root@ctier:~/test# sed
's/Atul/Mohan/' salary.txt
1001,Ajay,Manager,25000
101,Satish,Founder,30000
302,Mohan,CEO,26000
434,Raj,Senior Manager, 26000
1231,Kalyan,Human Resource,20000
root@ctier:~/test#
|
Note: We are not changing the file. Sed only changes
the display output not a file. If you want to ignore the case the use “I” option at end pattern. i.e.
‘s/Atul/Mohan/i’
Replace Satish with Pravin only on lines that contain thekeyword
'Founder':
root@ctier:~/test# sed
'/Founder/s/Satish/Pravin/' salary.txt
1001,Ajay,Manager,25000
101,Pravin,Founder,30000
302,Atul,CEO,26000
434,Raj,Senior
Manager, 26000
1231,Kalyan,Human
Resource,20000
root@ctier:~/test#
|
7. Replace the 1st occurrence of lower case “a” with upper case “A” in a line
root@ctier:~/test# sed 's/a/A/' salary.txt
1001,AjAy,Manager,25000
101,SAtish,Founder,30000
302,Atul,CEO,26000
434,RAj,Senior Manager, 26000
1231,KAlyan,Human Resource,20000
root@ctier:~/test#
|
Same command we can use for replace all occurrences of “a” in a line by upper case “A” with
below command:
root@ctier:~/test# sed
's/a/A/g' salary.txt
1001,AjAy,MAnAger,25000
101,SAtish,Founder,30000
302,Atul,CEO,26000
434,RAj,Senior MAnAger,
26000
1231,KAlyAn,HumAn
Resource,20000
root@ctier:~/test#
|
If you want to replace the second occurrence of “a” with “A” in each line
then use following syntax: sed 's/a/A/2' salary.txt
Sed flags in short:
i-
Ignore case
p- Print
w- Write
You can use this flags as per your need in sed
command.
8. Suppress the meaning of special characters in sed while mataching pattern. Use backslash to remove special meaning.
[root@rhel Documents]#
cat test.text
Hello How are you ?
Hello /usr/local/bin
directory used to store the commands script
[root@rhel Documents]#
[root@rhel Documents]#
sed 's/\/usr\/local\/bin/\/usr\/bin/g' test.text
Hello How are you ?
Hello /usr/bin
directory used to store the commands script
[root@rhel Documents]#
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9. Get matched pattern in “&”. Lets see the use of “&” operator.
Enclose
the employee id in [EMP ID] and show output.
[root@rhel Documents]# sed
's/^[0-9][0-9][0-9]/[&]/' salary.txt
[100]1,Ajay,Manager,25000
[101],Satish,Founder,30000
[302],Atul,CEO,26000
[434],Raj,Senior Manager, 26000
[123]1,Kalyan,Human Resource,20000
[root@rhel Documents]#
[root@rhel Documents]# sed
's/^[0-9][0-9][0-9][0-9]/[&]/' salary.txt
[1001],Ajay,Manager,25000
101,Satish,Founder,30000
302,Atul,CEO,26000
434,Raj,Senior Manager, 26000
[1231],Kalyan,Human Resource,20000
[root@rhel Documents]# sed -e 's/^[0-9][0-9][0-9]/[&]/' -e
's/^[0-9][0-9][0-9][0-9]/[&]/' salary.txt
[100]1,Ajay,Manager,25000
[101],Satish,Founder,30000
[302],Atul,CEO,26000
[434],Raj,Senior Manager, 26000
[123]1,Kalyan,Human Resource,20000
[root@rhel Documents]#
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10. Use execute flag (e). Run commands inside the files by sed command.
Suppose,
we add the ls –l command in file.txt file at starting of each line. Then we
want to run these lines then how to run :
[root@rhel Documents]# cat > file.txt
/etc/passwd
/etc/group
[root@rhel Documents]#
root@rhel Documents]# sed -i 's/^/ls -l /'
file.txt
[root@rhel Documents]#
[root@rhel Documents]# cat file.txt
ls -l /etc/passwd
ls -l /etc/group
[root@rhel Documents]# sed 's/^/ /e' file.txt
-rw-r--r--. 1 root root 1527 Mar 20 18:18
/etc/passwd
-rw-r--r--. 1 root root 786 Mar 20 18:18
/etc/group
[root@rhel Documents]#
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Sed has many more uses. This is
the basic sed commands use. I have given here most of the sed Command in Unix with examples. If you need more details you can post on my facebook page.
Very useful for quick revision of SED command.And SED is among the most important and useful command to go through...
ReplyDeleteUsing sed, write a script that takes a filename and a pattern to do the following.
ReplyDeleteIf the given pattern exists in the file with the very next line starting and ending with the same pattern, delete the line that starts and ends with the given pattern.
So after running on this file
=====================
hai people we had
a lot of fun
writing scripts
We will
have more
tomorrow
Hurray!
======================
should change ro
======================
hai people we had
writing scripts
We will
have more
tomorrow
Hurray!
======================
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