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my $stuff = 'file.txt';
open(F, "$stuff") || die "Can not open file: $!\n";
...
print "@records\n";
s/lastlineofdata//;  #This is the part I am struggling with
close(F);

use strict;
use warnings;
...
print $out_fh, @records;

$out_fh->close;

perl -pi -e 'last if eof()' file.txt