$infile = $ARGV[0];

open(IN, '<', "temp.in") || die "\nCan't open temp.in \n";
open(OUT, '>' "temp.out");
$/="";
while(<IN>)
{
    if($_=~s/(.*)&lt;p&gt;(.*)\<\/p\>(.*)//ms)
    {
        $pre =  $1;
        $par =  $2;
        $pos =  $3;

        $par=~s#\n# #ig;
        print OUT "$pre&lt;p&gt;$par\<\/p\>$pos";
    }
}
close(IN);
close(OUT);