Variable interpolation happens only inside double quotes. Change this ... to ...

And perhaps even better, change to the three-argument form of open:
    open my $fh, '<', $filename or die "Can't open '$filename': $!";
(no need to string-interpolate  $filename in  open call, quoting  $filename in error message makes all whitespace explicit).

In reply to Re^2: open file and write the content into another file by AnomalousMonk
in thread open file and write the content into another file by cesapun

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