Well, I think you're way overdoing it here.. if you're worried about efficiency and resources, you probably shouldn't be reading in the array at all.. there's no need. And, since you've already determined that $uclc is going to be either one of 'uc' or 'lc', you don't need the extra check in there..
Here's how I woulda done it..
#!/usr/bin/perl -w
 
use strict;
 
my $uclc    = shift or Usage();
my $infile  = shift or Usage();
my $outfile = shift or Usage();
Usage() unless ($uclc eq 'lc' || $uclc eq 'uc');
 
open (IN, "< $infile") or die "Error opening $infile for read: $!";
open (OUT, "> $outfile") or die "Error opening $outfile for write: $!"
+;

foreach (<IN>) {
  # just print directly on reading, easier on the mem..
  #  quicker too, and we know that $uclc is going to 
  #  be either lc or uc at this point.
  print OUT $uclc eq 'lc' ? lc() : uc();
}
 
close IN               or die "Error closing $infile after read: $!";
close OUT                or die "Error closing $outfile after write: $
+!";
 
######################################################################
+####
sub Usage {
   die "\n Usage: uclc.pl (lc|uc) infile outfile\n";
   }
######################################################################
+####

[download]
-Syn0

Update: didn't look too closely at opening code before, but fixed same bug after Hofmator mentioned it. Also, his elimination of the string equality check in the loop was a good call. ++

In reply to Re: More efficient munging if infile very large by synapse0
in thread More efficient munging if infile very large by ybiC

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