Just open another filehandler and print the lines into it.

my $infilename  = 'infile.txt';
my $outfilename = 'outfile.txt';

open my $infile, "<$infilename" or die "Unable to open $infilename $!"
+;
open my $outfile, ">$outfilename" or die "Unable to open $outfilename 
+$!";
while (<$infile>) {
  s/hue/someword/g;
  print $outfile $_;
}

close $infile;
close $outfile;
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