this is my code as of now.

#!/usr/bin/perl

use warnings;

my $html = shift;

my $htmlvar;
open(my $fh, '<', $html) or die "cannot open file $html";
{
    chomp;
    local $/;
    $htmlvar = <$fh>;
}
close($fh);

my $line = 1;

while (<STDIN>){
    chomp;
    if ($htmlvar =~ /$_/  && $htmlvar !~ /<sentence id\"[0-9]*\">$_<\/
+sentence>/){
        $htmlvar =~ s/($_)/<sentence id\"$line\">$1<\/sentence>/;
        $line++
    }
}

print "$htmlvar\n";
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