Learning Perl, 5th Edition

Answers to Chapter 13 Exercises

1. Here’s one way to do it, with a glob:

   print "Which directory? (Default is your home directory) ";
   chomp(my $dir = <STDIN>);
   if ($dir =~ /^\s*$/) {         # A blank line
     chdir or die "Can't chdir to your home directory: $!";
   } else {
     chdir $dir or die "Can't chdir to '$dir': $!";
   }
   
   my @files = <*>;
   foreach (@files) {
     print "$_\n";
   }

   First, we show a simple prompt and read the desired directory, chomping it as needed. (Without a chomp, we’d be trying to head for a directory that ends in a newline—legal in Unix, and therefore cannot be presumed to simply be extraneous by the chdir function.)

   Then, if the directory name is nonempty, we’ll change to that directory, aborting on a failure. If empty, the home directory is selected instead.

   Finally, a glob on “star” pulls up all the names in the (new) working directory, automatically sorted in alphabetical order, and they’re printed one at a time.

2. Here’s one way to do it:

   print "Which directory? (Default is your home directory) ";
   chomp(my $dir = <STDIN>);
   if ($dir =~ /^\s*$/) {         # A blank line
     chdir or die "Can't chdir to your home directory:
   $!";
   } else {
     chdir $dir or die "Can't chdir to '$dir': $!";
   }
   
   my @files = <.* *>;       ## now includes .*
   foreach (sort @files) {   ## now sorts
     print "$_\n";
   }

   Two differences from the previous one: first, the glob now includes “dot star”, which matches all the names that do begin with a dot. And second, we now must sort the resulting list because some of the names that begin with a dot ...