inplace file replacement for nth pattern match

Question

I have a file with many lines but I can summarise my requirements like below:

            <DT><A HREF="http://127.0.0.1:1234/ABCDE/wp-admin/index.cfm?event&msg=secure&fr=sp">Wonderland(Site 3)</A>
            <DT><A HREF="http://127.0.0.1:5678/FGHIJ/wp-admin/index.cfm?event&msg=secure&fr=sp">abc (test)</A>
--
            <DT><A HREF="http://127.0.0.1:1234/ABCDE/wp-admin/index.cfm?event&msg=secure&fr=sp">Wonderland(Site 3)</A>
            <DT><A HREF="http://127.0.0.1:8303/CFIDE/administrator/index.cfm?event&msg=secure&fr=sp">xyz (Prod)</A>
--
            <DT><A HREF="http://127.0.0.1:1234/ABCDE/wp-admin/index.cfm?event&msg=secure&fr=sp">Wonderland(Site 3)</A>
            <DT><A HREF="http://127.0.0.1:8303/CFIDE/administrator/index.cfm?event&msg=secure&fr=sp">lmn (Prod)</A>

I have to insert a new line after first occurrence of:

<DT><A HREF="http://127.0.0.1:1234/ABCDE/wp-admin/index.cfm?event&msg=secure&fr=sp">Wonderland(Site 3)</A>

similar to it e.g.

<DT><A HREF="http://127.0.0.1:2323/xnmp/wp-admin/index.cfm?event&msg=secure&fr=sp">NewSite(Site 4)</A>

insert a new line after second occurrence with another variable line similar to above and so does after third line match.

I have tried something like this with various combinations but it is not working:

input1='<DT><A HREF="http://127.0.0.1:1234/ABCDE/wp-admin/index.cfm?event&msg=secure&fr=sp">Wonderland(Site 3)</A>
output1='<DT><A HREF="http://127.0.0.1:2323/xnmp/wp-admin/index.cfm?event&msg=secure&fr=sp">NewSite(Site 4)</A>'
output2='<DT><A HREF="http://127.0.0.1:2324/xnmp/wp-admin/index.cfm?event&msg=secure&fr=sp">NewSite(Site 4)</A>'
output3='<DT><A HREF="http://127.0.0.1:2124/xnmp/wp-admin/index.cfm?event&msg=secure&fr=sp">NewSite(Site 4)</A>'
gawk -i inplace -v in2="$input1" -v voutput1="$output1" '/in2/{c++;if(c==1){sub(in2,in2 "\n" voutput3);c=0}}1' a  ; where a is my file name

I am able to replace all using sed but not individually. Working one which replaces all:

sed -i.bak "s#$input1#$input1\n\t\t$output1#" a

Expected output:

            <DT><A HREF="http://127.0.0.1:1234/ABCDE/wp-admin/index.cfm?event&msg=secure&fr=sp">Wonderland(Site 3)</A>
            <DT><A HREF="http://127.0.0.1:2323/xnmp/wp-admin/index.cfm?event&msg=secure&fr=sp">NewSite(Site 4)</A>
            <DT><A HREF="http://127.0.0.1:5678/FGHIJ/wp-admin/index.cfm?event&msg=secure&fr=sp">abc (test)</A>
--
            <DT><A HREF="http://127.0.0.1:1234/ABCDE/wp-admin/index.cfm?event&msg=secure&fr=sp">Wonderland(Site 3)</A>
            <DT><A HREF="http://127.0.0.1:2324/xnmp/wp-admin/index.cfm?event&msg=secure&fr=sp">NewSite(Site 4)</A>
            <DT><A HREF="http://127.0.0.1:8303/CFIDE/administrator/index.cfm?event&msg=secure&fr=sp">xyz (Prod)</A>
--
            <DT><A HREF="http://127.0.0.1:1234/ABCDE/wp-admin/index.cfm?event&msg=secure&fr=sp">Wonderland(Site 3)</A>
            <DT><A HREF="http://127.0.0.1:2124/xnmp/wp-admin/index.cfm?event&msg=secure&fr=sp">NewSite(Site 4)</A>
            <DT><A HREF="http://127.0.0.1:8303/CFIDE/administrator/index.cfm?event&msg=secure&fr=sp">lmn (Prod)</A>

Answer 1

Instead of storing in variables, put all the outputs, one per line, in a file, say outf Then do this:

$ sed -e "\\#${input1}#R outf" a

This assumes you are using GNU sed. Once you are satisfied of the changes, then bring in the -i option.

Explanation:

° Alternate delimiter needs to escaped by a backslash. In our case, # is the delimiter, so we escape it with a backslash.
° Wait a minute but I see two of them here, you'll be asking. Well coz, before what we write on the command line gets to sed is seen n processed by the shell. So since backslash is special within double quotes, we need to double it so that after shell has seen it, it shall be presented as one to sed. So the Universe is happy.
° Now comes the R command. This is a nonstandard command given by Gnu folks,  and is precisely what the doctor ordered for your scenario. It will print one line each time it is invoked and place that line after the current input line is printed.

******** /Fini.