Here is some commented code for you to perform what you were aiming for with your pseudo code. Set the $base_dir var and it will run as is.

cheers

tachyon

#!/usr/bin/perl -w
use strict;

# specify the full path to the image files in $base_dir
# do not use \ on win32 use / Perl will convert like magic!
# \ is the escape char. Just *don't use it* for paths
# use / and let Perl take care of the conversion.
  
my $base_dir = 'c:/windows';

# first let's just read all the files in the dir
# and print them out, this is how we do it:

opendir (DIR, $base_dir) or die "Unable to open dir: $base_dir Perl sa
+ys: $!\n";
while (my $file = readdir DIR) {
    print "found file $file\n";
}
closedir DIR;

# OK so now we can read all the files in a dir
# we can look at doing stuff with them.
# What we do is to stuff the files into the
# arrays you wanted using "push"
# we push them into the array if they match
# the criteria you seem to want
# Note that within a match m/ / the . char has a special
# meaning (it matches any single char) so to match a 
# literal . we "escape" it with a backslash (backwhack)

my (@image4by6, @screenres, @thumbnail); # pacify strict
opendir (DIR, $base_dir) or die "Unable to open dir: $base_dir Perl sa
+ys: $!\n";
while (my $file = readdir DIR) {
    push @image4by6, $file if $file =~ m/4 by 6\.tif/;
    push @screenres, $file if $file =~ m/screen res\.tif/;
    push @thumbnail, $file if $file =~ m/thumbnail\.jpg/; 
}
closedir DIR;

# now lets print out our sorted arrays
# via a function that we define (a subroutine)

print "\n\nImage4by4 array contains:\n";
print_sorted( @image4by6 );

print "\n\nScreenres array contains:\n";
print_sorted( @screenres );

print "\n\nThumbnail array contains:\n";
print_sorted( @thumbnail );

exit;

# this sub takes one argument - an array
# the array is passed to the sub in the 
# magical @_ array. We sort this array
# storing the result in @sorted
# we then use a loop to iterate over
# each element assigning it to $file
# we print each file in turn plus a newline \n

sub print_sorted {
    my @sorted = sort @_;
    foreach my $file (@sorted) {
       print "$file\n";
    }
}
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