use IO::File;
use LWP::Simple;

##</code><code>##


open(INPUTFILE, "< input.txt") or die "cannot open file for reading $!";
open(OUTPUTFILE, "> output.txt") or die "cannot open file for writing $!";
..... code goes here

close INPUTFILE;
close OUTPUTFILE;

##</code><code>##

while(my $line = <INPUTFILE>) {
    $line =~ s/&+/&amp;/; # Assuming you have a good reason for this
# See $line has now been declared, where before it wasn't
    my ($isbn, $ocln, $title, $author, $call_number) = split(/\t/, $line);# See the variables have been declared
    # .. do something here
}