You have a couple of bugs in your regex. You are missing the closing '/'.

You need an e flag to evaluate the substitution expression. However as it stands that gets messy because of the mixture of string litteral characters and characters that represent a calculation. No way Perl can disambiguate that!

I'd be inclined to do it like this:

use strict;
use warnings;

my $str = "<tag1>Complete</tag1><tag2>3386</tag2><tag3>77844</tag3><ta
+g4>11</tag4><tag5>30</tag5><tag6>4.7</tag6>";

if ($str =~ m|<tag1>Complete</tag1>|) {
     $str =~ s|(?<=<tag6>)(.*?)(?=</tag6>)|$1 * 100|e;
}

print $str;
[download]

Prints:

<tag1>Complete</tag1><tag2>3386</tag2><tag3>77844</tag3><tag4>11</tag4
+><tag5>30</tag5><tag6>470</tag6>
[download]

Note the use of strictures (use strict; use warnings;). The regex uses a look behind and a look ahead assertion to anchor the capture group so that the replaced text is only the number. The /e then gets the calculation done in the substitution.

Hi rsriram, try like this,

use strict;
use warnings;

my $str = '<tag1>Complete</tag1><tag2>3386</tag2><tag3>77844</tag3><ta
+g4>11</tag4><tag5>30</tag5><tag6>4.7</tag6>';

if($str =~ /<tag1>Complete<\/tag1>/i)
{
$str =~ s/<tag6>(.+?)<\/tag6>/"<tag6>".( $1 * 100 )."<\/tag6>"/ei;

}
print $str;
[download]

Updated

Typo error in your replacement statement. Use 'e' option modifier for execute the statement in the replacement part.

See the documentation for further clarification perlre

This looks like it might be easier to do with something like XML::Simple and manipulate the data directly and rewrite it out to disk. Just an idea....