B.6 Dynamic Behavior

22. 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

23. 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 $@ .

24. 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"

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

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