in reply to Adding <pre> at beginning </pre> at file end

Here is another way 

use strict;
use warnings;
open (FILE,"+<","test");
local $/=undef;
my $a=<FILE>;
$a =~ s/^(.*)$/<pre>$1<\/pre>/gs;
seek(FILE,0,0);
print FILE $a;

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But you have to be careful when the file size is huge

--Lakshmanan G.

The great pleasure in my life is doing what people say you cannot do.

In Section Seekers of Perl Wisdom