I was working on a certain project last week where I need to insert a line after the match in 100 of files in Linux or Unix operating system. I found that inserting a line after a match using sed is easy. It was pretty successful for me, so I thought I will share this on my blog.
Let’s take an example to understand it
We have an html file like below
$ cat test.html
<html>
<head>
<title>This is test</title>
</head>
<body>
This is test page
</body>
</html>
sed add line after match
I need to enter certain text Welcome everybody after like <body> in the file
we can achieve it using sed with append
sed -e '/<body>/aWelcome everybody' test.html <html> <head> <title>This is test</title> </head> <body> Welcome everybody This is test page </body> </html>
So far the above command just changes the output. The file is not changed. If you want to change the file also
we can do this -i option
#sed -i -e '/<body>/aWelcome everybody' test.html #cat test.html <html> <head> <title>This is test</title> </head> <body> Welcome everybody This is test page </body> </html>
If you want to preserve leading space at the start of the new line
#sed -i -e '/<body>/a / /Welcome everybody' test.html #cat test.html <html> <head> <title>This is test</title> </head> <body> Welcome everybody This is test page </body> </html>
You can make these changes in multiple files using * or giving a pattern to the file
sed -i -e '/<body>/aWelcome everybody' *.html
sed multiple line after match
You can do using \n operator as given below
sed -e '/<body>/aWelcome everybody\nWelcome everybody' test.html <html> <head> <title>This is test</title> </head> <body> Welcome everybody Welcome everybody This is test page </body> </html>
sed add line before match
if I need to enter certain text before like <body> in the file
#sed -e '/<body>/i Welcome everybody' test.html
<html>
<head>
<title>This is test</title>
</head>
Welcome everybody
<body>
This is test page
</body>
</html>
So far the above command just changes the output. The file is not changed. If you want to change the file also
we can do this -i option
#sed -i -e '/<body>/i Welcome everybody' test.html #cat test.html <html> <head> <title>This is test</title> </head> Welcome everybody <body> This is test page </body> </html>
sed insert after line number
This is easier, you just need to specify the line number. If you have insert after line ,below command can be used
#cat test.html <html> <head> <title>This is test</title> <body> This is test page </body> </html> #sed '2a Welcome everybody' test.html <html> <head> Welcome everybody <title>This is test</title> <body> This is test page </body> </html>
If you want to do before the line number
# sed '2i Welcome everybody' test.html <html> Welcome everybody <head> <title>This is test</title> <body> This is test page </body> </html>
Hope you like this short article on sed add line after match, sed add line before match, sed insert after line number. Please do let me know your feedback
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