The scripts in this site have been tested with GNU sed version 4.0.5, these scripts may result in incorrect results when using older versions of GNU sed.
Using GNU sed version 4.0.5, you can use '\n' to denote a newline character in
  • a character class, and
  • the replacement part of the substitution command 's'.
This feature conforms to 'the single UNIX specification, version 2 of the Open Group, where the sed specification says:
The escape sequence '\n' matches a newline character in the pattern space. A literal newline character must not be used in the regular expression of a context address or in the substitute command.
In versions of GNU sed prior to 3.02.80, you have to use '\' followed by an ENTER to express a newline character in the replacement part of command 's'. For example, to add a newline character to the end of every line, changing from
Line 1 AAA
Line 2 BBB
Line 3 CCC
Line 4 DDD

to be
Line 1 AAA

Line 2 BBB

Line 3 CCC

Line 4 DDD

you have to use
s/$/\
/
when using older versions of sed, while you can just use
s/$/\n/
in GNU sed version 4.0.5.
Source codes of GNU sed can be found at
ftp://ftp.gnu.org/gnu/sed.