how to delete line from the XML file

Question

how to delete only the line from xml file ( with sed/awk or perl one liner line )

that start with:

<units> 

and ended with

</Networks>

as the follwoing

<units><unit ip= ............   </units><ranges/></Networks>

Answer 1

Do not use regular expressions to parse XML. It's an excellent way to create brittle code, because there's a bunch of perfectly valid things you can do with XML which will break a regex. Things like reformatting the XML in entirely valid ways (such as 'pretty printing' it in a nested/indented form) will break your code.

Instead I would suggest - use an XML parser. Personally, I like the XML::Twig module in perl.

Your comment suggests that what you're trying to do is add stuff to a <Networks> element in your XML.

So how about something like this:

#!/usr/bin/perl
use strict;
use warnings;

use XML::Twig;

my $xml_text = '<XML>
<Networks><units><unit ip="1.2.3.4" /></units><ranges/></Networks>
</XML>';

my $parser = XML::Twig->new( 'pretty_print' => 'indented' );
#would probably use 'parsefile' instead here
$parser->parse($xml_text);

print "\nBefore:\n";
$parser->print;


#insert a new element into 'Networks':
$parser->root->first_child('Networks')->insert_new_elt(
        'last_child',     #position - end of "Networks" element
        'new_element',    #element
        {   'attribute_here'    => "value_here",
            'another_attribute' => 'another_value',
        },                 #attributes as key value pairs
        "Content_here",    #element content
    );


print "\nAfter:\n";
$parser->print;

Answer 2

Try this:

perl -i -pe 's|^<units>.*</Networks>$||' /my/filename

Note that if you have leading or trailing space in the line you will need this instead:

perl -i -pe 's|^ *<units>.*</Networks> *$||' /my/filename

I uesd pipe as a separator rather than slash to avoid unnecessary escaping.

Answer 3

Since you indicate that you are aware that this will break your XML, you can do what you want with one of these:

1. Perl

   perl -ne 'print unless m#^<units>.*</Networks>$#' file.xml 
   perl -ne 'm#^<units>.*</Networks>$# ? next : print' file.xml 
   

2. awk

   awk '!/^<units>.*<\/Networks>$/' file.xml 
   

3. sed

   sed '/^<units>.*<\/Networks>$/d' file.xml 
   

4. grep

   grep -Ev '^<units>.*<\/Networks>$' file.xml 
   

5. Bash (and zsh), for the sake of completion

   while read -r line; do 
       [[ "$line" =~ ^\<units\>.*\<\/Networks\>$ ]] || printf "%s\n" "$line"
   done < file.xml