Learning Perl, Fourth 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 you don’t need to keep the list of lines 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 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 the range 1 to 7.

   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";

   To get the output on separate lines, do it this way:

       print sort <STDIN>;