How do I insert a newline/linebreak after a line using sed - bash

Question

It took me a while to figure out how to do this, so posting in case anyone else is looking for the same.

Answer 1

For adding a newline after a pattern, you can also say:
sed '/pattern/{G;}' filename
Quoting GNU sed manual:
G
Append a newline to the contents of the pattern space, and then append the contents of the hold space to that of the pattern space.
EDIT:
Incidentally, this happens to be covered in sed one liners:
# insert a blank line below every line which matches "regex"
sed '/regex/G'

Answer 2

This sed command:
sed -i '' '/pid = run/ a\
\
' file.txt
Finds the line with: pid = run
file.txt before
; Note: the default prefix is /usr/local/var
; Default Value: none
;pid = run/php-fpm.pid
; Error log file
and adds a linebreak after that line inside file.txt
file.txt after
; Note: the default prefix is /usr/local/var
; Default Value: none
;pid = run/php-fpm.pid
; Error log file
Or if you want to add text and a linebreak:
sed -i '/pid = run/ a\
new line of text\
' file.txt
file.txt after
; Note: the default prefix is /usr/local/var
; Default Value: none
;pid = run/php-fpm.pid
new line of text
; Error log file

Answer 3

A simple substitution works well:
sed 's/pattern.*$/&\n/'
Example :
$ printf "Hi\nBye\n" | sed 's/H.*$/&\nJohn/'
Hi
John
Bye
To be standard compliant, replace \n by backslash newline :
$ printf "Hi\nBye\n" | sed 's/H.*$/&\
> John/'
Hi
John
Bye

Answer 4

sed '/pattern/a\\r' file name
It will add a return after the pattern while g will replace the pattern with a blank line.
If a new line (blank) has to be added at end of the file use this:
sed '$a\\r' file name

Answer 5

Another possibility, e.g. if You don't have an empty hold register, could be:
sed '/pattern/{p;s/.*//}' file
Explanation:
/pattern/{...} = apply sequence of commands, if line with pattern found,
p = print the current line,
; = separator between commands,
s/.*// = replace anything with nothing in the pattern register,
then automatically print the empty pattern register as additional line)

Answer 6

The easiest option -->
sed 'i\
' filename