mjhjmtu

I have a similar content in a file. I have a list of line numbers with me say 1,2, 4.

1. Can feed all the required line #s


2. Extract the contents between the first occurence of and last occurence of </book>
   

Data:

</p><p>abc</p></book><book><p style="text-indent:0em;">def</p></book><book><p>ghi</p><p style="text-indent:0em;"></book><book><div><p> 
</div><p>123</p></book><book><p style="text-indent:0em;">456</p><p>789</p><p style="text-indent:0em;"></book><book><div><p> 
<div><p>nothing !!!</p></div> 
</p><p>ABC</p></book><book><p style="text-indent:0em;">DEF</p></book><book><p>GHI</p><p style="text-indent:0em;"></book><book><div><p>JKL</p></div></book><div> 

Input Line #s: 1, 2, 4 (Which I want to feed in the command)

Desired Output:

<book><p style="text-indent:0em;">def</p></book><book><p>ghi</p><p style="text-indent:0em;"></book>
<book><p style="text-indent:0em;">456</p><p>789</p><p style="text-indent:0em;"></book>
<book><p style="text-indent:0em;">DEF</p></book><book><p>GHI</p><p style="text-indent:0em;"></book><book><div><p>JKL</p></div></book>

1) Extract specific lines

In your four-line example to extract the 1st, 2nd and 4th line would be easy by deleting the 3rd line:

sed 3d file

But your file is probably more complicated, so a more general solution would be to do

sed -e 1b -e 2b -e 4b -e d file

So for each line that should be kept you jump to the end of the script with b and delete all remaining files.

For a longer list of line numbers you may want to generate the script:

sed $(for i in 1 2 4; do echo "-e $ib"; done) -e d file

But it seems that it's not about the line numbers, but whether there are <book>s on that line. If this is true, you better forget about the line numbers and do

sed '/<book>/!d' 

2) extracting the contents

Greedy * of regexp is not a friend for tasks like this. That's why my personal version of sed has an option o to the s command to replace only by the matched part:

sed '/<book>/!d;s_<book>.*</book>_&_o' 

But this won't work for you, so you need some more regex juggling:

sed '/<book>/!d;s_<book>_n&_;s_.*n__;s_(.*</book>).*_1_' file

If your version of sed doesn't support n in the replacement string, use an actual newline (escaped by a backslash):

sed '/<book>/!d;s_<book>_
&_;s_.*n__;s_(.*</book>).*_1_' file

With perl:

#!/usr/bin/env perl

use strict;
use warnings;

use v5.10;

my @lines = (1, 2, 4);

while(<>) 
 next unless $. ~~ @lines;
 chomp;
 s#.*?(<book>.*</book>).*#$1#;
 say