Perl says the -s is confusing. It also says "Unterminated <> operator". Look for where you've got a -s and an < together, and you should be able to trim it down to:

C:\temp>perl -e "print -s <= 2"
Warning: Use of "-s" without parentheses is ambiguous at -e line 1.
Unterminated <> operator at -e line 1.
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Go and add some disambiguating brackets, and everything is happy. For example

C:\temp>perl -e "print -s($_) <= 2"
1
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    push @files , grep { -f  && -s >= $min_size && -s <= $max_size "$d
+/$_" } read_dir($d);
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There is no operator between -s <= $max_size and "$d/$_", and you can't modify the return value of grep anyways.

You are stating the same file three times when you only need to stat it once.

You need something like either:

    push @files, grep { -f && -s _ >= $min_size && -s _ <= $max_size }
+ read_dir( $d, prefix => 1 );
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Or:

    push @files, map { -f "$d/$_" && -s _ >= $min_size && -s _ <= $max
+_size ? "$d/$_" : () } read_dir( $d );
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Try adding parenthesis, as indicated by the error message. I've not tried it, but I'd suggest starting with:

   push @files , grep { -f  && (-s >= $min_size) && (-s <= $max_size) 
+}
                 map  { "$d/$_" } read_dir ($d);
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Note: I've added the map bit, as it looks like that's what you were wanting.

...roboticus

When your only tool is a hammer, all problems look like your thumb.

Still getting the same issue message:

Warning: Use of "-s" without parentheses is ambiguous at test.pl
line 19.
Unterminated <> operator at test.pl line 19.
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Never mind ... apparently today I'm an idiot...

Reading the documentation reveals that -s doesn't return a number. Instead, it indicates whether has nonzero size. If you need to know the file size, you'll have to use a suitable function to read the file size, and *then* compare it.

...roboticus

When your only tool is a hammer, all problems look like your thumb.

Based on what you posted, this:

push @files , grep { -f  && -s >= $min_size && -s <= $max_size "$d
+/$_" } read_dir($d);
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becomes:

push @files , map { "$d/" . $_} grep { -f  && ( -s >= $min_size) && (-
+s <= $max_size) } read_dir($d);

#this is untested.
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Maybe this modification? I've assumed, that you'll need full path/file-names (see read_dir() in File::Slurp):

  ... 
  push @files, grep { -f  and  -s $_ >= $min_size  and  -s $_ <= $max_
+size }
               read_dir( $d, prefix => 1 );
  ...
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...} # loop

my $c = @directories;
...
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