sed - 匹配多行并在匹配上方插入

Question

I have a file that looks like this

#multi
#line
#comment
$var1=foo

#multi
#line
#comment
$var2=bar

#############################################
#   END                                     #
#############################################

using sed (since i am already using sed in other places in my script and i would prefer to remain consistent) how can I match the "END" section ie one or more comment marks followed by a coment + space + END and then add the following lines before the end section

#############################################
# user login
#############################################

server.user=$USER
server.pswd=$PASSWD

<newline>
<newline>

please comment you answer so I can learn and hopefully not need to ask a followup question

thanks !

Answer 1

 sed '/^##* END$/i\
# user login\
#############################################\
\
server.user=$USER\
server.pswd=$PASSWD\
\
\
#############################################' input

This takes advantage of the fact that the header block of the END section is only one line and is the same as the header of the inserted block so that we are re-using the first line of the END section as the first line of the header of the new section, and writing a new first line for the END block header. The i command tells sed to insert text before the buffer is printed, and the escaped newlines allow us to insert multiple lines of text.