if (scalar @titles > scalar %titles) {   # no, some basenames are n
+on-unique
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scalar @titles will almost always be greater than scalar %titles

$ perl -le'
my @x = "a" .. "z";                                           
$x{ $_ }++ for @x;
print for scalar @x, 0 + @x, scalar %x, 0 + %x;
'
26
26
19/32
19
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You need to use the keys function:

   if ( @titles > keys %titles ) {   # no, some basenames are non-uniq
+ue
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Thanks for spotting that! I tested it on the unique basenames case, not the case where pathnames differ only. Here's the corrected code:

#!/usr/bin/perl
# COLUMNS - Copyright (C) 2008 Xenoscience, Inc. - Released under GPL 
+v3
# SSF 101808 - display files in columns side-by-side

use integer;
use strict;
use Getopt::Std;
use Term::Size 'chars';

my (%opts);
my ($cols,$rows)=chars;

getopts('d:htw:',\%opts);
unless (@ARGV or $opts{h}) {
   print <<EOT;
Usage: columns [-d delimeter] [-h] [-w width] file file ...
      Print files in properly spaced columns for the terminal width

   -d C    Delimiter between columns (defaults to spaces)
   -h      This help display
   -t      Display file names as titles (base names only if all unique
+)
   -w N    Assume N character width per line
EOT
   exit 1;
}
$opts{d}||=' ';
$opts{w}||=$cols;
$cols=$opts{w};

my (@cols,$arr,$col,$row,$wd,$file,$len,$line,$maxrow,$spacer,
    @titles,%titles);
for $file (@ARGV) {
   $col=get_basename($file);
   push @titles,$col;
   $titles{$col}++;
   $arr=[];
   open(FILE,$file) || die "$file: $!";
   while (<FILE>) {
      chomp;
      push @$arr,$_;
      $len=length($_);
      $wd=$len if $len>$wd;
   }
   close FILE;
   $maxrow=scalar @$arr if $maxrow<scalar @$arr;
   push @cols,$arr;
}

# compute spacer
$spacer=($cols/@cols)-1;
$wd=$spacer if $spacer>$wd;
$spacer=($cols/$wd);
--$spacer while ($spacer>0 and @cols*($wd+$spacer)-$spacer>$cols);
$spacer=$opts{d} x $spacer;

# titles
if ($opts{t}) {
   # determine if titles can have pathnames chopped off
   if (scalar @titles > scalar keys %titles) {  # some same names
      @titles=@ARGV;
   }
   $col=scalar @cols;
   for $file (@titles) {
      $line=(' ' x ($wd/2-length($file)/2)).$file;
      print $line.(' ' x ($wd-length($line)));
      --$col;
      print $spacer if $col;
   }
   print "\n";
   $col=scalar @cols;
   for $file (@titles) {
      print '=' x $wd;
      --$col;
      print $spacer if $col;
   }
   print "\n";
}

# content
for ($row=0; $row<$maxrow; ++$row) {
   $col=scalar @cols;
   for $arr (@cols) {
      $line=$arr->[$row];
      print $line.(' ' x ($wd-length($line)));
      --$col;
      print $spacer if $col;
   }
   print "\n";
}
exit;

sub get_basename {              # extract basename from url or path
   my $path=shift;
   my $i=rindex($path,'/');
   $i>-1 ? substr($path,$i+1) : $path;
}
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