Learning Perl, 5th Edition

Answers to Chapter 3 Exercises

1. Here’s one way to do it:

   print "Enter some lines, then press Ctrl-D:\n"; # or maybe Ctrl-Z
   @lines = <STDIN>;
   @reverse_lines = reverse @lines;
   print @reverse_lines;

   …or, even more simply:

   print "Enter some lines, then press Ctrl-D:\n";
   print reverse <STDIN>;

   Most Perl programmers would prefer the second one, as long as they don’t need to keep the list of lines around for later use.

2. Here’s one way to do it:

   @names = qw/ fred betty barney dino wilma pebbles bamm-bamm /;
   print "Enter some numbers from 1 to 7, one per line, then press Ctrl-D:\n";
   chomp(@numbers = <STDIN>);
   foreach (@numbers) {
     print "$names[ $_ − 1 ]\n";
   }

   We have to subtract one from the index number so that the user can count from 1 to 7 even though the array is indexed from 0 to 6. Another way to accomplish this would be to have a dummy item in the @names array, like this:

   @names = qw/ dummy_item fred betty barney dino wilma pebbles bamm-bamm /;

   Give yourself extra credit if you checked to make sure that the user’s choice of index was in fact in the range 1 to 7.

3. Here’s one way to do it if you want the output all on one line:

   chomp(@lines = <STDIN>);
   @sorted = sort @lines;
   print "@sorted\n";

   …or, to get the output on separate lines:

   print sort <STDIN>;