Learning Perl, 6th Edition

Appendix A. Exercise Answers

This appendix contains the answers to the exercises that appear throughout the book.

Answers to Chapter 1 Exercises

1. This exercise is easy since we already gave you the program.

   print "Hello, world!\n";

   If you have Perl 5.10 or later, you can try say:

   use 5.010;
   say "Hello, world!";

   If you want to try it from the command line without creating a file, you can specify your program on the command line with the -e switch:

   $ perl -e 'print "Hello, World\n"'

   There’s another switch, -l, that automatically adds the newline for you:

   $ perl -le 'print "Hello, World"'

   The quoting on Windows in command.exe (or cmd.exe) needs the double quotes on the outside, so you switch them:

   C:> perl -le "print 'Hello, World'"

2. The perldoc command should come with your perl, so you should be able to run it directly.

3. This program is easy too, as long as you got the previous exercise to work:

   @lines = `perldoc -u -f atan2`;
   foreach (@lines) {
       s/\w<([^>]+)>/\U$1/g;
       print;
   }

Answers to Chapter 2 Exercises

1. Here’s one way to do it:

   #!/usr/bin/perl -w
   $pi = 3.141592654;
   $circ = 2 * $pi * 12.5;
   print "The circumference of a circle of radius 12.5 is $circ.\n";

   As you see, we started this program with a typical #! line; your path to Perl may vary. We also turned on warnings.

   The first real line of code sets the value of $pi to our value of π. There are several reasons a good programmer will prefer to use a constant^[400] value like this: it takes time to type 3.141592654 into your program if you ever need it ...