Advanced Perl Programming

Dynamic Behavior

1. Symbolic references:

   $i = "foo";
   $$i = 10;             # Sets $foo to 10
   ${"i"} = 10;          # Sets $foo to 10
   &$i();                # Calls foo();
   push (@$i, 10, 20);   # Pushes 10,20 into @foo

2. Run-time expression evaluation:

   while (defined($str = <STDIN>)) {
       eval ($str);
       print "Error: $@" if $@;
   }

   This is a tiny Perl shell, which reads standard input, treats $str as a small program, and puts the compilation and run-time errors in $@.

3. Dynamic substitutions. Use the /e flag for the s/// operator, to specify an expression instead of a pattern:

   $l = "You owe me 400+100 dollars";
   $l =~ s/(\d+)\+(\d+)/$1 + $2/e;
   print $l; # prints "You own me 500 dollars"

4. Module and object method invocations (see also #20 and #21):

   $modulename->foo(); # Calls foo() in the module indicated by
                       # $modulename