my $infile = qq{PSR_Date.txt};
my $outfile = qq{PSR_OutputDate.txt};

open( my $infh, q{<}, $infile ) or die qq{Can't open '$infile' to read: $!\n};
open( my $outfh, q{>}, $outfile ) or die qq{Can't open '$outfile' to write: $!\n};

while( defined( my $line = <$infh> ) ) {
  ## ...
  print $outfh $line;
}
close( $infh );
## Note that depending on OS, amount written, buffering, phase of moon you might not see output in the file until you do this.
close( $outfh );